The first person they told was Lestrade. He was the logical choice, seeing as he would begin wondering about Sherlock's coordination issues, and likely assume drugs. It was awful. John told him. Alone. Told him not to treat Sherlock any differently (like that was gonna happen). Lestrade didn't believe him. Thought it was a joke, and an awful one at that. But John's face didn't waver, didn't smile, didn't speak the words Lestrade was hoping for. 'It's all a joke.' Nope. Those words never came.
Lestrade looked like he wanted to cry. He did that night when he went home, sobbing on the couch for the army doctor who was watching the world's only consulting detective die. And even if John said they weren't a couple, they obviously had feelings for each other. Anyone could see that. He cried for John and he cried for Sherlock and he cried for Mrs Hudson losing one of her boys. And lastly, he cried for himself. And in the morning, he got up like nothing had happened and called Sherlock up for a case.
They didn't want to tell Mrs Hudson. They didn't want to hurt her. It was the last thing anyone wanted. But Mrs Hudson was strong. She had proved that when she was attacked by the Americans and after Sherlock's 'death'. (Sherlock was right about what he'd said about her. England would fall if she left Baker street.) Her boys meant so much to her. So John made excuses as long as he could (It's an experiment. Poison. Nerve damage. Pretending. Hurt on a case. I don't even know.) Until it was no longer a possibility of hiding it.
John told her. Sherlock never wanted to be there when other people found out. Didn't want the pity, the tears, the attempts at comforting.
John teared up a little as he told her.
Mrs Hudson held him, warm and motherly smelling like biscuits and sorrow.
She didn't cry until the next day making squares. She pulled them out of the oven with her potholders. They slipped and she watched, detached, as a blister formed.
She only realized she was crying when a tear dropped onto her reddened hand. She collapsed into a chair and sobbed over the kitchen table.
When she got up after running out of tears, she realized that she had dropped the squares on the floor. She left them there for two days.
Mycroft knew. No one ever figured out how, but he knew.
They got home one day from a case and he was in their flat. Simply sitting in John's chair. Sherlock didn't even blink. John felt a tiny flame of rage but doused it when Mycroft stood up and moved away from his seat.
"Ah Mycroft. Diet doing poorly I see. I suppose you've heard I'm dying."
"Naturally," Mycroft replied stiffly, staring down at his umbrella.
John glanced between the two, wondering if he should leave.
"No, you can stay," both brothers said at the same time. They glared at each other. John was terrified. He decided to sit on the couch, out of the blast radius if something were to happen.
"So?" Sherlock continued.
"Can an older brother not stop by when he hears that his younger sibling has less than six months to live?" Mycroft's gaze was still sweeping the carpet.
"Yes, they can," Sherlock replied tersely, "except when they're you."
Mycroft's eyes snapped up to meet Sherlock's.
"Alright," he said softly, and yet somehow there was more rage in this than in most screams from soldiers that John had heard. "If you do need anything, you know how to contact me."
Sherlock snickered as Mycroft exited the room.
John was still a bit shocked.
"How... how did he know?"
Sherlock shrugged, then pushed John off the couch so he could sit on it.
"I've told you many times John, he is the British government. And the British government," he whispered, "knows everything."
John could hardly argue with that.
Sherlock insisted there was no one else worth telling.
"Molly?" John suggested.
"Oh."
Which was how John ended up in the morgue that afternoon with Molly sobbing into his chest while he looked, rather detached, at a dead body. John wondered how he died.
He went home later after Molly ran out of tears and apologized profusely for both the overly emotional display and the tear stains on his jacket.
Molly cried so much the next two days that she thought she might die of dehydration.