I have a theory that I am sure you might like. I accepted the fact that Michael is the Foxy Bully. This is just a theory I've made to add to Michael's story.
I think that William Afton planned the whole thing. The only reason why Mike bullied his younger brother is because William Afton TOLD him.
In the Midinight Motorist minigame, we play as what is assumed to be William Afton after he killed Henry's daughter (this was assumed due to how the source code for Midnight Motorist says "Later that night") we see Mike sitting and watching TV. Mike says: "Leave him alone. He had a rough day." Now if this is Mike/Foxy Brother, why would he say that? If anything, he would let Mr. Afton yell at the Crying Child all the time. But then it hit me:
What if Mike DIDN'T WANT to bully him? It seems like Mike was defending him. Why? Out of guilt? Who knows. But yet it seems like the Midnight Motorist minigame seems to connect to FNaF 4 very closely.
"Run off to that place again."-Mr. Afton "You know what will happen if he catches you."-Fredbear plush
I assume the Crying Child's death was more than just a prank or a accident. Mike killed his brother because William Afton forced him to do it. Due to how abusive William can be to his own children, it seems very likely Mike bullied his brother out of fear and wanting attention. Plus, since we see moniters and footages of the FNaF 4 house. It seems like Mr. Afton was making sure the Crying Child stays inside his room, or face the consequences.
I have been working on a fanmade sequel to the Twisted Ones along with a fanmade novel specifially for the main story in the games' themselves. So far all I've got is that Charlie's mother is the lady in the red dress and I also kinda wanted Michael Afton to have a more reacurring role but he's not quite the same as he was in Sister Location. I wonder what you think so far.
For some reason, I just cannot stop drawing William Afton lately. I usually make him as he was depicted in the novels. Mosttly because I am not a huge fan of drawing a purple stick figure with white eyes.