I am no expert but I do question the tactic of avoiding dangerous things like stairs based on unscientific anecdote of my own experience. Both my parents live upstairs in a two story house. My Dad still drives, which terrifies me. He recently started a drive from San Francisco to Los Angeles with my sister in the car who took over after a bout an hour, understandably. My Dad retired from work reluctantly at 90. They do a bunch of things that worry me but they are also 92 and 91 and living active independent lives. So there is some value in the risk taking.

I do think there is science to back up the idea that as your parents get older it is really helpful for them to have younger friends. For my Dad this came through work, for my Mom through friends who enjoyed concerts and plays. The point is to try to get them to have a connection with younger people. It's depressing, but my Mom says all her original friends have died off. For your parents it could be a hobby, taking care of grand kids, etc.