I only see a few options for how this will end, and I doubt it will be good for any of them;
Ben is either sent to jail for the Exterminator's death and for Violet's, or at least covering up and hiding her death. Or Ben is killed by a ghost or by his wife or constance.
Wife will either stay locked up in the hospital or come back to the house only to continue to get driven crazy and is sent back permanently shortly after that. I don't think she'll be killed.
My personal guess; Ben confronts Constance and says he's going to take care of Tate(or he'll call the cops or something), and Constance ends up killing Ben. At the same time, Burned guy spills that he killed deformed attic kid on Constance's behalf. Cops go to arrest Constance and find she has killed Ben, then they find some of the bodies around the house. Wife, still locked up in the hospital, gives birth to her twins. One of them is obviously evil. Wife dies in childbirth.
But hell, I'm not very good at guessing stuff with this show.