Marcus is already dead, and part of the story will involve Zeke being strung along to save his life, only to discover it is too late.
Logan will reappearThe writers of the previous film are returning and the story is said to be set within the world of the original films, so it would only make sense if they brought him back for this film. However, he will be revealed not to be the killer. In fact...
The copycat killer is not an Apprentice.
Mark Hoffman has returned.The new killer has been noted as targeting cops, which Hoffman was so there's a link there. And we never see if Hoffman dies in the bathroom so the writers could bring him back.