(insert city here), only to learn they are not the house's only inhabitants."
This plot line describes half of the horror movies ever made.
Why do people fall for these same story lines over and over again?
Yeah! I'm thinking the same thing! How come no one knows about a haunted house until a different family moves in? What did the previous home occupants do about it? How did they manage to cope living with nasty ghosts for years?
Unless a priest can successfully exorcise a house of its ghosts and demonic infestations, the best thing to do is raze the house completely.