The idea of both possessing one animatronic has never sat right with me. I know it was in one of the Fazbear Fright books but I never believed in it.

I think Fredbear and Golden Freddy are different suits with different souls. The crying Kid from game 4 possesses Fredbear whereas Cassidy possesses Golden Freddy

We already know that some animatronics will have different parts, different suits even. We see alternate mascot heads and stuff in the Parts & Service room of the first game.

In the bad ending of FNAF 3, there are 5 heads lit up representing the 5 kids. Why would both Fredbear AND Golden Freddy exist in UCN if it was the same suit? Fredbear being there is just part of the torture while Cassidy, Golden Freddy, is pulling the strings (as seen by the ending). She is the one Afton "shouldn't have killed".

In Happiest Day, they celebrate the FNAF 4 kids birthday that went wrong years ago. Thats why there's another colorless Freddy head - it's a Fredbear head. He passes on. We know the Princess Quest games are about Cassidy since that's the sprite name of the character. So she is freed there.

Fredbear never kills us in any of the games because the spirit possessing him, FNAF 4 kid, has no reason to. He was bitten in a prank gone wrong and not murdered. So he just kinda lurks. Cassidy, on the other hand, does have a reason to kill though.

In the FNAF 3 Springlocking when there's 5 kids teaming against Afton, it's not 6 spirits there, it's 5. And that's because Fredbear is a separate suit somewhere else having no reason to fight Afton.