Okay, so in Matpat's video reguarding the fnaf books and Ruin DLC, he says that 9 children disappeared, but there's only 6 animatronics, though sun/moon could count as 2 since the split personalities thing. But, that would still leave 2 souls left.
My theory is that those other 2 souls would be occupying Glamrock Bonnie and either Glamrock Foxy or Gregory himself.
(I understand the controversy of Gregory being a robot or not, so please don't attack me for it)