Hi! I hope he is feeling better, and on the road to a full recovery!
I have been several times last week or two (or both - one trip was 15 nights last two weeks of August). Although it is hot and humid, I like the lower crowds!
My daughter (with whom I am going this trip solo as a few others like last year this time, last week of August) has a connective tissue disorder that makes walking long distances very painful (we learned that one trip a year and a half ago when her shoulder subluxed, or partially dislocated) so we rented a wheelchair the last 3 trips.
I find a wheelchair so easy to maneuver. It's fine if it gets rained on a bit, but we do check an app on my iPhone ("my radar" - it is free so it's nice to see what is coming our way)
If you can push him in a wheelchair, maybe you'd want to do that? I don't know - only times it's hard for me (I'm almost 50) is going uphill a couple spots, like from Future World to France in Epcot - but it's fine really!
Yes, do keep an eye on the sky! I'd get the app! The storms are more often short lived, but can come down with a vengeance. We just take things in stride, and use a
DAS for her (she can't often stay out long, as I'm sure your DH can't so look into asking about that, as also she can't wait standing in line, so they used to give us a little shaded area to wait like for Haunted Mansion, since she could pass out).
It does cool things down sometimes in the evening after showers -we've had to get hoodies to keep us warm in the evenings in August!
Make sure you are aware of the indoor areas near you ahead of time! Also not sure where you're staying, but if you take a bus, go to the head of the line where they have either a marked spot that looks like a separate area or often it has the handicapped marking - the driver will load you both first so he's set and strapped in before they load the other passengers. That has been a lifesaver for my daughter!