Okay I just had to put this down and try to connect the fourth game to to the rest of the lore when I had this thought that I'm surprised hasn't been discussed yet.

I will start from the begining of the games and get to in in chronological order of events.

The events at five nights at freddy's four take place at the family diner possibly between the time spring bonnie and fredbear was active and was replaced by the four animatronics we came to know. Meaning all six at that time were active considering the plushies of the four animatronics from the first game. We learned that the child we are playing as was the bite victim and that 87 might not be the year it happened but was said 87 because of what happened to Jeremy at the end of the second game. The lore of the fourth game is as much as I can tell this.

The child has a upcoming birthday but has to deal with a bully of a older brother who's constantly playing mean pranks on him. During the night we see the child has to face nightmarish versions of the original four animatronics and golden freddy.

But here is where I have to put in reality for the sake of the lore as well as one of my theories of the fourth game. We know the four guys that was seen around the child are wearing masks of the animatronics so maybe instead of animatronics at night during what was really known as memories warped by fear into nightmares it was actually the child's brother and his three friends scaring the child every night. We know that around this time period a child was murdered outside the diner by the purple guy aka the murderer. But the fact the child didn't survive the bite given by fredbear thanks to the child's brother and his friends tormenting him on his birthday and placed his head in the jaw of the animatronic in the first place. For timelines sake I'm saying the fourth game is in 83 for the year four years before the second game meaning that sometime between this and the reopened pizzaria was when fredbear now known as golden freddy and spring bonnie were decommissioned from service. Thus turning the diner to the pizzaria.

Now in the second game taking place in 1987 we learned that the guard before the player was actually the murderer and was moved to the day shift. Through mini games we had learned about the first intended murder of the series at the diner by the purple guy. And that on Wednesday the murderer disguised himself in a golden suit which we now know was the suit that would later become springtrap. He killed four kids during a party and I noted that they had the same masks as the four from the fourth game as we found out with the give life minigame. Here's my thoughts about this. It is possible that the four kids that was murdered was in fact the same four that killed the child four years before and that the puppet/marionette is posessed by the Spirit of the child while fredbear is controlled by the Spirit of the other murdered child during the diner time period. The murderer flees after tampering with the animatronics such as the new 'toy' animatronics where a second bite happened in the companies history.

Six years later the events of the first game start with the pizzaria on its last legs and was closing in a week with the original four animatronics controlled by the four murdered kids confused the night guards as the one who killed them. During the second game we learned that the marionette was also in this smaller location. During the time the pizzaria was closed the murderer returned and using a mascot costume lured the animatronics to a hidden safe room and dismantled them freeing the spirits of the four kids which alongside the spirit inhabiting golden freddy huanted the murderer into the safe room and chased him. In desperation the murderer hid in the suit he used to kill them and did something really idiotic. He moved around while it was storming. In the third game we learned fredbear and spring bonnie were hybrid suits being bot mascot costumes and animatronic with spring locks. In the third game we learned the locks fail in certain conditions involving moisture. This made the suits dangerous. The locks failed and the animatronic inside the suit rushed to fill the suit crushing the murderer and getting lodged in his body killing him and making the suit unable to be removed. It was revealed that he befell the same fate as his victims posessing the very suit that killed him. As his corpse was taking the place of the endoskeleton he had become a literal zombie and with the cybernetics technically made him a cyborg.

Thirty years later the third game happened when springtrap was discovered and brought to fazbear frights. Where after a week the place due to faulty ventilation and wiring burst into flames and burned to the ground with only a few things untouched in the fire. That's as much as I can remember of the story and how each game is connected.

So yeah there's two theories I'm surprised hasn't been considered by now. Let me know what you think.