how to tell very touchy people who are not accustomed to listening to anyone about anything that they may be letting themselves in for more than they can cope with.
So you're saying they're not going to listen to you. So don't tell them what to do. Avoid anything like "you should..." or "If I were you..." Maybe try causal stories about your experiences, or questions neighbours could have.
I would assume they're older than you, and have probably lived there longer than you, so they should know what to expect and don't see a problem with it. But if they really haven't been through a whole winter, then the questions/conversations below might help warn them without saying "you're too old for this, get out of here," which might be honestly true, but exceedingly rude.
You could ask them some questions about shared winter preparations:
- If they want to split the cost of having the shared driveway plowed, or hiring someone to shovel the walkways
- Want to split buying some emergency wood / propane / food (even if it says "good for 10 years" you don't really want to eat any after 1 or 2 ;-)
- If they have an emergency generator you could use, or if you have one then if they want to buy their own cord & you'll share a few hours of power?
- If you're having any winter prep work done to your house (having a generator transfer switch / outside plug installed, or a new roof or sidewalks) ask if they're interested too, the contractor will already be there & maybe give them the same price?
If they're being friendly & have lived there a very long time, you could try asking them what winters were like when they were young, or if they remember any particularly large storms. That might jog their memory. Or maybe they grew up in Alaska and have no fears from experience? Could be a good time to share your winter storm stories too, and could get them thinking.
Saying you're thinking of leaving for January and asking where they usually spend winters & how it's better/worse than Florida/Arizona/California is another idea, you could talk a little about what you don't like about the snow & work you have to do.
Or the next time their family stops by, walk over and talk to them & ask their family who will be taking care of them for the winter, and ask them some of the same questions above. If their family is concerned, then let them try convincing the very touchy people. You can get an emergency contact name & number too, just in case, and if it's someone new try calling them to a) confirm and b) ask the same questions.
I'm not sure how active they are, but some 97 & 87 year olds don't get out much anyway. If it'll only be "bad" for a few weeks they might just stay in & not even notice? If they are very active, then telling the story about the winter you were stuck in your house for a week (if that happened)