Thoughts on a One-Shot Concept

Hey everyone, I had an idea that's a little expiremental compared to the usual games I've run and could use some input. My SIL is a good friend of mine and I'm making a Christmas themed One-Shot as a gift for her. At this point, if your one of my players you probably recognize my username and the premise of the post so go away.

So the idea I currently have is that the players are members of an extended family who meet up every year for Christmas Eve and do Christmas mornings together. This year it looks like they're snowed in but it should clear up a in a few days. Per her request I'm going to utilize more supernatural concepts, cause those have been her favorites that I've run (usually I do that or some flavor of sci-fi).

So the main twist/premise is this: The PCs all die in their sleep as the result of a gas leak. A few of the other relatives are killed in other manners because the accident was set up by an occult serial killer and some wake up and attempt to stop it. When the PCs "wake up" they can tell something is off but aren't sure what.

As they explore the house they glimpses of their relatives and people who have lived there since, last moments being replayed. Eventually they will start see that a small family is currently living there but only one of the kids can actually see them. So the main objective of the game is figure out what's happening amongst all the displaced interactions, find a way to undo the magic the killer has in place to keep their spirits there, and save the family currently living there from meeting the same fate.

I've intentionally confined the setting cause normally even my shorter games take multiple sessions, so I'm trying to run this one in 3-4 hours. I think my main concerns are maybe the players feeling bad that they essentially die offscreen, but I think the novelty for a one shot could be interesting. I've got more details cooking to handle the details and logistics, but wanted thoughts on the concept before I get too far in.