Thank you for the replies.
Wish there were a cooler time of the year, but there practically aren't. Thailand (our chosen location) is 35 C most of the year - and 32 C during the so called cold season. Still, it sounds good that you have actually been to the tropics even though you have MS.
We have thought about the vests, etc. ourselves, so that will definitely be something my mother should try out. Maybe we can even borrow/rent some locally in the tropics, so we don't have to find and buy them (we and my mother live in Europe, so we have to pay a massive amount for postage from US).
No matter what, I think the most important thing is that my mother can get through the 'death zones' (from airport to car, car to house, etc.). She do of course want to see the country we live in, but I believe the most important thing for her is to see her grandchildren, children and the home we live in.
Are wheelchairs or other transport available at the airport? I don't know about
Thailand, of course, and when I went to the Philippines I took my own manual chair. Here in the US wheelchairs are available at the airports, and porters will push people from their planes to cars. She might see if she could rent a manual wheelchair in her home country and use it when she comes to visit, just for those times when she does have to walk a lot -- like inthe airport, or car to house, or shopping, or whatever. She can take it on the plane with her, and have it available when she comes to visit.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....