Welp, you might like this.

So, i clearly am going to explain why...you heard the title, you know at this point. So, look at Revenant Freddy and look at Revenant Bonnie A K A Thomas, (Thomas posseses Revenant Bonnie,) look at their faces each one of them has one of their eyes missing, and also they are names Revenants, and revenant means, a person who has returned from the dead, and Thomas the protagonist of Post Shift 1, is the one who posseses Revenant Bonnie. Do you see why he is so focused on? Now, about Revenant Freddy, i don`t know who that guy is, presumably another random guy? Now, move on to Remnant Chica and Remnant Foxy. Now, remnant means "A part or quantity that is left after the greater part has been used, removed, or destroyed." which do you remember my Revenant Chica Post Shift 2 theory, where i proposed the theory that Revenant Chica was early version of Subject 3 Chica? Well, i presume Remnant Foxy went throught pretty much the same thing, where he got replaced and locked away and broken for experments on him being unsucseesful. So, that`s my fan explanation. But, don`t take this as a 100% true, none of this is confirmed.