It sounds like this potential house move would be basically a negative move. They'd move because they can't deal with their current house, or can't get around, or they need more care due to illnesses. There's also the immense negative of the entire process of moving, looking for somewhere, sorting out, big bills, upheaval, which is a negative for everyone but at their age will hit 300% harder. You can visualise the positives (a new, easier place to live, lots of cash realised both for them and you) but I think visualising positives that don't exist yet is much harder when you've older, especially when they only exist on the other side of a huge pile of negatives. Tbh if they don't find it possible to go to the cafe round the corner, just going to look at houses will be a mountain to climb.
Expecting people to do things that are negative for them is a big ask. And imo the results are unlikely to be the broad sunlit uplands. That doesn't necessarily mean you shouldn't keep trying, but do acknowledge how unbelievably challenging it all looks for them.
My mum's move at 83, which was heavily promoted and underpinned by me and my sister, probably started aged about 80. Really she would just have put her house on the market and taken it off again multiple times, left to herself. We found that embarrassing, but with hindsight i will neber again feel any concern about inconveniencing an estate agent. Making any decision at all was much harder for her, and who can blame her because she was leaving a house and a life she adored for entirely negative reasons. And frankly it all cost a bomb and she was permanently miserable with the outcome. I wish she hadn't done it, mostly.
I would regard the house move as a topic of conversation, not a plan. Just say 'I'll help you whenever you want to do it' and leave it.