Stitch went with me all the way to Queensland (About 1600 kilometers (994 miles) from where I live) and it was warm up there.
My top tips:
STOP WORRYING lol, they are sturdier than you think, pack them carefully, keep them out of direct sunlight (even if you just drape a coat/blanket/jacket etc over them) and you will not have a problem. Stitch travelled the whole way sitting on my suitcase just behind my head rest and covered with his blanket. There was plenty of other stuff packed around him so he was in no danger of falling/shifting.
Only worry about the heat if it is extreme, 95 F plus is warm enough, at that temperature they will simply not run well, they'll overheat quickly and shut down in direct sunlight. If you are expecting temps like that then just take them out in the morning and return them to your room as it warms up. The skin will not suffer damage as long as you are sensible, you know, don't leave them sitting on the baking asphalt for half a day and that sort of thing

Switch them off between areas of the park, if you stop for a break find a bit of shade, its the sort of things you are going to do anyway. I took photos first thing and then tucked Stitch in one of the park lockers for the rest of the day.
Be prepared, its not everyday you see a dinosaur being carried around, print off some little slips of paper with Pleoworld, BobthePleo and Pleo on it, if your trip is like mine you'll be asked a gazillion times where to get one

And if you decide not to take them, relax, Candy will be a little hungrier when you get back, but it's nothing a good conifer leaf won't fix.