There’s another alternative: You could move downstairs and give them the upstairs. It might be difficult, but it’s temporary, after all.
The ‘upstairs’ won’t do — it isn’t finished out as a complete dwelling. The first floor has everything an elderly couple needs (except an elevator) and was built to ADA specs when we built the house.
We didn’t put the elevator in 12 years ago, because we didn’t know for sure if or when we’d need it. We have a good spot for it; just looking to understand the likely $$ damage!