Joke sequel to Spider-Man No Way Home. Spoilers ahead if you haven't seen it.
In the Amazing Spider-Man Universe
Peter-Three otherwise known as The Amazing Spider-Man was busy at work on a machine in his garage. He had recently been on a rather thrilling adventure that took him to another universe where he met two alternate versions of himself. They were like him, but at the same time very different. The experience made him want to see if there were more versions of him in other universes and this device would allow that to happen. He'd spent the last few months dedicating his leisure moments to theories on the multi-verse. Thus far he had been unsuccessful. The purpose of the machine was to create a portal that would drag him into a world with an alternative version of himself.
He'd had a recent breakthrough though. He theorised that if he used his own DNA, he'd be able to pull himself into a world with an alternative version of him. He was at the testing stage, and he wanted to test his machine sooner rather than later. He activated the machine and a bright red portal appeared in his garage.
"It works," said Peter-Three taking of his glasses.
Peter-Three was walking towards the portal, when something went wrong. The portal should have simply let him walk through, but suddenly he felt a great force of wind pulling him forward. Knowing this wasn't supposed to happen, Peter-Three tried sticking to the ground, so he could crawl back and turn off the machine. Unfortunately, his ability to stick to surfaces and his superstrength was overpowered by the force of the machine. Unable to do anything Peter-Three fell headfirst into the portal, which shut behind him once he was through.
In the MCU
Peter-One, one of the Peter's Peter-Three had met during his multiverse journey was swinging through the streets of New York. He was the youngest of the three, being only seventeen and now that the entire world had forgotten of his existence he was all alone. He was about to swoop in and stop a bank robbery, when an identical red portal opened above him. Like Peter-Three, Peter-One did his best to resist the force of the portal. He shot a web at a nearby building and tried to pull himself towards it. Peter-One pulled as hard as he could, but like Peter-Three, the force of the portal was too strong. He lost his grip and fell through the portal into another dimension.
In the Rami-verse
The oldest of the Peter's, also known as Peter-Two was enjoying a quiet night out with his partner Mary-Jane Watson. Their lives had been complicated over the past decade, but they had found a way to make it work and they were happy. Like the two Peter's before him, Peter-Two was also caught off guard by the sudden appearance of the red portal. He two immediately felt it pulling him in. Unlike the other two, he gave minimal resistance. He had a feeling that nothing he did would be able to stop him from falling through. He could however save the woman he loved. As the only one of the three Spider-Men who could spin organic web he knew what he had to do.
"Mary-Jane, I have to go I'm sorry," said Peter-Two, before webbing her to a nearby tree so she could be safe from the portal.
"Peter, be careful," pleaded Mary-Jane.
"I'll be back. I promise," said Peter-Two, before disappearing into the unknown.
The three Peters fell through a large red void. They had no idea where they would end up, but they knew it wouldn't be their home. What was most odd however, was that they could fill something about them changing as they fell through the portal. They were de-ageing. Before long all of them landed in a massive room with a stone floor. Each of them had de-aged to that of an eleven-year-old and they found they were amongst a crowd of children around the same age. All these children were wearing identical black robes. It was as if they had fallen into some odd boarding school. The Peters quickly noticed that they too were now wearing these black robes. The three Peters looked around this room. There were four long tables each of which housed a different group of students. There was also a head table which sat a row of oddly dressed adults, one of which was ginormous in size. The Peters figured they were the teachers. There were also banners on the ceiling that housed different animals surrounded by different colours. One was scarlet and gold with a lion, another was green and silver with a serpent, another was yellow and black with a badger and the final one was blue and bronze with an eagle.
As the Peters were thoroughly inspecting their new area, it didn't take them long to spot each other. Although all of them had been de-aged, they recognised each other immediately. Peter-Three approached Peter-One.
"Peter?" asked Peter-Three, wanting to confirm his suspicions.
"Peter," said Peter-One.
"Hey guys," said Peter-Two joining the group. "I didn't think I'd see you guys again so soon."
"Neither did I," said Peter-One.
"Have you been messing with magic again?" asked Peter-Two, remembering the circumstances of how they met last time.
"No, this had nothing to do with me. I was just swinging through New York when suddenly I found myself being sucked into a giant red portal," said Peter-One.
"This was my doing," confessed Peter-Three.
The other two Peter's looked at him with shock.
"What did you do?" asked Peter-Two angrily.
"I'll tell you later. I think the first thing we need to do is figure out where we are," said Peter-Three.
"I think I know where we are," said Peter-One. "We're in Harry Potter."
"I'm sorry, we're in what?" asked Peter-Three.
"Harry Potter," repeated Peter-One.
Both Peter-Two and Three looked at One with confusion.
"Do you guys not have Harry Potter in your worlds?" asked Peter-One.
Peter-Two and Three shook their heads.
"Wow, ok I'm gonna need to explain a lot to you guys," said Peter-One.
"Explain what?" asked Peter-Two.
Before Peter-One could respond an announcement was made by one of the teachers.
"Now before we begin, Professor Dumbledore would like to say a few words," said a tall female teacher with a Scottish accent wearing a green dress.
Peter-Two and Three thought it would be important to listen in, but Peter-One told them he could fill them in on all the details later. He did however tell them that the name of the Scottish teacher was Professor McGonagall. Peter-One went on to explain the world of Harry Potter. How it was a story about an orphaned boy who discovered he's a wizard that survived an attack from the evillest wizard of all time when he just a baby. This wizards name was Lord Voldemort. Ten years later he got a letter informing him that he had been accepted into Hogwarts School of Witchcraft and Wizardry, where his parents learnt magic. It didn't take Peter-Two and Three long to figure out that their current location was Hogwarts.
Peter-One then told them that there were seven books in total and if his guess was correct, they were currently in the first story, otherwise known as the Philosopher's Stone. He followed up this explanation with how each book presented Harry with a different challenge he had to overcome in his fight against Voldemort.
"I thought you said he defeated Voldemort when he was a baby?" asked Peter-Two.
"Through some complicated magic that's not revealed until the 6th book he managed to survive," said Peter-One.
"Well, you did say he's the evillest wizard of all time, it makes sense that he'd have a back-up plan," said Peter-Three.
Suddenly a sound was heard that caught their attention.
"Gryffindor!"
The three Peters turned to the front of the hall and saw that it was a talking old hat that had spoken. It had been placed on the head of a girl with brown hair and buck teeth who was now going down to join one of the tables.
"Gryffindor? What's that?" asked Peter-Two, as they watched a blonde boy with a pointed face take a seat next to the teacher holding the hat.
Peter-One didn't get a chance to respond before they heard the hat say, "Slytherin."
"Now I have the same question about Slytherin," said Peter-Three. "And what's with the talking hat?"
Peter-One had a feeling they'd have to wear the hat sooner or later, so felt he'd better tell the other Peters about the Hogwarts houses. He explained that the hat was called the Sorting Hat and that it sorted the students into one of four Hogwarts houses, named after the four founders, based on the personalities of the students. The houses were Gryffindor, Slytherin, Hufflepuff and Ravenclaw. Gryffindor favoured students that were brave and daring, Slytherin took those who were cunning and ambitious, Ravenclaw took students who were intelligent and wise and Hufflepuff was a house of loyal and hardworking individuals.
Peter-One then told them that every year there was a house cup competition for the students. Triumphs would earn them points, while rule breaking would cause them to lose points and the house with the most points at the end of the year would win the house cup.
Peter-Two and Three found this fascinating. Peter-One felt that maybe he should also explain Quidditch to them, but felt that was something he could leave for later. The Peters started discussing the different houses, but were unable to voice which house they'd want to be in.
"Peter Parker?" asked Professor McGonagall.
The three Peters looked at each other. Which one of them was she referring to.
"Peter Parker," asked Professor McGonagall a second time.
The three Peter's still didn't know who should go first.
Professor McGonagall then looked at her list and saw that there was a total of three Peter Parkers on the list of new students.
"Who among you are Peter Parker?" asked Professor McGonagall.
The three Peters raised their arms.
"Please decide amongst yourselves the order in which you should be sorted," requested Professor McGonagall.
They decided that Peter-One should go first, because he was the only one that knew anything about this world and because he was referred to as Peter-One. They felt this sorting process was good in a way, because all three of them were the same person from a different universe. From that logic they all believed they would be sorted into the same house. They felt this was good as it would allow them to stick together while in unfamiliar territory. Unfortunately, they were in for a shocking surprise.
Peter-One sat down as Professor McGonagall put the sorting hat on his head. Just like what he read in the books he could hear the Sorting Hat speaking to him.
"Hmm, right. A very loyal individual. A real team player. Not to mention extremely hard working," said the Sorting Hat before announcing. "Hufflepuff."
Peter-One went to sit down with the Hufflepuff students, hoping that the other Peters would be joining him soon.
Peter-Two was the next of the Peters to take a seat. Professor McGonagall put the hat on his head, unaware that they were all in for a major surprise.
"Hmm, a brave one, a very brave one. One who's willing to jump headfirst into a fight and not for fame or glory, but because it's the right thing to do," said the Sorting Hat before announcing, "Gryffindor."
The three Peters were shocked. Why was Peter-Two sorted into a different house to Peter-One? They were the same person. Sure, they looked different, had different lives, and slightly different backstories, but they were the same person. Knowing that it wasn't a good idea to make a scene, Peter-Two went down to sit with the Gryffindor kids.
Now it was Peter-Three's turn to wear the sorting hat. He sat on the stool and Professor McGonagall placed the hat on his head.
Like the two Peters before him, Peter-Three could hear the Sorting Hat whisper in his ear.
"Hmm, a smart one, a very smart one. You're very curious aren't you. You've come here all for the sake of seeing new things and learning new skills. If you're here simply because of your quest for knowledge," said the Sorting Hat who then announced. "Ravenclaw."
Peter-Three went to sit with the Ravenclaw students.
The three Peters were very confused by what had transpired. They were alternate versions of each other and yet they'd all been sorted into different houses. How was this possible?
Before long a huge feast appeared before them. The Peters spent the entirety of the feast trying to figure out why they'd been sorted onto different houses. They'd need to work together if they wanted to get out of this predicament, which would be a lot harder now that they'd have to spend a lot of time separated from one another.
Eventually, they were called away by their house prefects along with the rest of the first years, so they could go to their common rooms. Having been unable to talk in secret during the feast, the Peters agreed to meet up the next afternoon after classes were finished. They needed a way home. Peter-Three had a lot of explaining to do.