You can always take a Freudian psychotherapeutic approach. "Tell me, demon, about the relationship with your father."
Yes! That is exactly how the story ends. The last sentence in my draft is: "The beast would never be fully banished, we knew, for we would catch glimpses of it, stalking about the house reminding us that it would remain with us for all of our days." That likely won't be the very last sentence, but I appreciate endings, especially in horror/thriller, when the problem isn't 100% solved. I was just having trouble thinking up a reckoning moment, when the family finally decides to confront the demon. Naturally, I thought of exorcism to try to drum up ideas but I never intended to fully get rid of the monster, because psych/emotional demons are never rid of, they just fade into dormancy, we ideally learn to cope with them. Thank you for your input!
I like what Maggie May said. Early 20th century was full of particular ignorance and hate but older folks passed down stories. So finding that particular person who can handle that family member would be good. Maybe there is a talisman or family heirloom that the rest of the family doesn't know of.