Please point out all the issues I will have to take into consideration for my AU where William is innocent and was mentally controlled by SpringBonnie’s AI into committing the horrors he later became known for. [FNaF is insanely huge...]

The premise is this one and I’ve been thinking about it for a while now.

I tried watching FNaF videos to better understand exactly which points in the story I would need to be more careful with when writing and addressing them. However, the more I tried to find answers, the more questions popped up, such as the degree of canonicity of details from the books, the ambiguity of character names (like the Crying Child, whom some say is Evan, others say Garrett, and some even say Dave), the ambiguity around the identity of "The One You Should Not Have Killed" (which many speculated to be Cassidy, while others more recently speculate it could be Andrew), the forgotten and overlooked DCI (Dead Children Incident) that happened in 1987 and which Scott never really addressed satisfactorily outside of FNaF 2, as well as its more metanarrative treatment as being less relevant than the MCI (Missing Children Incident), the issue of how exactly Agony and Remnant work and their limits, and finally, I’ve seen some comments about how the franchise’s story is more "headcanon" than actual canon (what exactly are these headcanons, so I can distinguish them from canon?), and some people complaining that FNaF has had retcons along the way.

Well, I'm new to the community. So, I don't know everything about the franchise yet. Plus, I'm still saving up to buy the games and the books.

If anyone could clarify the canon issues that my AU needs to deal with, I would really appreciate it.