I disagree about your last point. Talking ghosts can absolutely be scary if it’s done right. The Exorcist demon is pretty famous for both frightening people and never shutting up, and demons and ghosts often serve similar purposes in horror movies. It could have easily been framed as a ghost possession instead of a demonic possession.
Well being dark doesn’t automatically make something a horror story to be fair, does it have horror elements or presentation? Like does it try to frighten or at least unnerve the audience purposefully?
My grandma could have mustered a single jig and one day of walking in her 90s. She definitely would not have been able to work a part time job. I think you just want an excuse to hate grandpa Joe, so you invent one even though on proper scrutiny it doesn’t hold up to reality. But you don’t need to justify hating someone, you’re allowed to just hate them for no good reason. Instead of throwing all old people under the bus for the sake of hating Joe, just let the hate flow through you without needing to find a reason for it.
He only has to be a billionaire playboy for a few hours then he can pretend to get blackout drunk at a party or something and sleep for the rest of the day.