The women at the end (Possible Spoiler)

So, at the end when the family go to the Grandma's house, are the women that Dennis is running from (including the Grandma) possessed or are they witches? Surely 'Toby' isn't possessing them all? Was Grandma evil all along? And if it was all about a coven of witches (who are apparently all female) how come Toby is in league with them? Why is he helping them? Did I miss the part where any of this was explained or was it not? Also, in the movies predecessors, Katie and Kristie are still the protagonists - I forget if, in either of the first two movies, the events of the ending of PA3 are discussed e.g. who raised them after Julie and Dennis died? Did the Grandma stay evil/possessed? Forgive my ignorance if I am just being stupid and missing something key. I just didn't really understand the end.

All I can say is I was Enchanted to meet you...