I’d haul them myself and take a look at them whenever you stop for gas and food, but it depends on how good you are at driving a horse trailer. Are you good at hauling? Are you calm and take turns and stops slowly? Is your trailer safe and well equipped? Water is always a concern. You can flavor your water troughs with something that you can take on the road and use at the overnight stop and at rest stops. I used ACV, but many use a little powdered drink mix.
When I was in the USN, my 26 year old mare went coast to coast with me a month after colic surgery. When she was 30, we went from Virginia to Rhode Island and back. She did fine.
The horse who gets the runs on hay…he might need some senior feed watered down. It seems like the old ones have trouble with their teeth properly chewing the hay and that’s what causes diarrhea. Our old gelding had issues with that and we switched him to a watered down senior feed diet and he did great. He could eat pasture grass, but the hay would too course and long.
The one with ataxia…what does your vet recommend? That sounds like it could be bad in a trailer.