The ultimate explanation!
Whats so hard to figure out?
1:The father had an affair with babysitter Anne
2:THATS why he had apicture of the house and why they said he had been there before with his daughter (Anne)!and thats whythe akwardly look at eachother..
3: The whole family Freudstein are dead aka ghosts, thats why Freudstein isnt in the cellar all the time, He is probably in another "Ghostly" realm connected to the house.
4:Mae and her mother "rescues" Bob at the end by taking him to a spirit realm, He probably also was killed but we didnt see his "passing"..
Hope this claryfies any thoughts, Sorry for the spelling,broken keyboard+Swedish ;)
AND I dont think Freudstein could be classified as a regularZombie, More like a ghost/revenant...
If you want to make me puke, play some Rap music