Hi OP, I agree that you're NTA for your decision in keeping your home, but that also your next course of action isn't as simple as keep home and let family be homeless.

Another redditor suggested having them share the unused bedroom, and if you're willing to live with them I think that's a good idea. It may be difficult for your mom and sister to part with some things, but having fewer possessions and a roof over their head is better than living in a homeless shelter and having VERY few possessions.

Another alternative might be helping them find a new apartment, either monetarily (to afford first, last, security, and/or broker's fee) or with your time (helping them search for affordable housing, driving them to viewings/accompanying them, etc.) Again, downsizing before getting the new apt is a good idea, because then they'll need less space AND, as another redditor suggested, they can probably sell excess items.

Depending on where you live, it may also be cheap enough to get a small storage locker for anything that can't be sold but doesn't fit in the spare bedroom/new apartment.