Theorizing here. And some of it contains spoilers.
Sister Location literally happens during FNAF3. It makes a ton of sense after listening to phone guy talk about the 'sister location' and the incident. And Sister Location reveals it's FNAF3 that comes after because we see Spring Trap followed by 'Fazbears Fright' which happens to be 'Fazbear's Fright Entertainment in FNA3 where you're working at as a security guard after Sister Location is closed down. Therefore, I'm no longer skeptical about it. Of course, the little girl that died in Sister Location is related to Michael Afton. And Michael Afton had a younger brother because in FNAF4, we see the bite of 87 incident. I'm not a hundred percent sure if FNAF4 happened before or after FNAF3 & Sister Location at the same time.
FNAF Pizzeria aka FNAF4 + FNAF Sister Location + FNAF3 [All of this seems to happen in 1983 or 87]
Still working out how the murderers work with purple guy. If there's more than one purple guy. But I don't really want purple guy to be innocent as a lot of theorist seem to claim right now because, I disagree. (I need to watch Sister Location again too.)
And if William Afton was the original killer or not. Unless we count the Silver Eyes book to be canon, then he would be. However, he went into the Spring Trap suit in the book and eventually dies in it. So part of the canon might not be entirely right unless the Spring Trap was left for a time, cause Afton had to change in order not to get caught despite being suspected as the murderer. And Silver Eyes takes place in Fazbear's diner and eventually pizzeria/pizza. (I forgot which.) So Henry having his son die by William Afton would make sense if this does tie into FNAF2 first murder with the fifth boy being potentially Golden Freddy. Although some argue it's the Puppet. Again, Silver Eyes seems far fetched in some ways despite being canon to a degree. It's very confusing just thinking about it on my own.
I don't know what to make of it all. xD
Update 1/17/2017
It's also possible it might not be Afton. Perhaps it's Henry's kids that are involved.