It's really up to you if you want to use their cups or mason jars. I used their cups and it was a ten day journey.
I had 2 gallon jugs with pre-treated water but it froze in the backseat, so I just used Canadian hotel water for the changes. Just make sure you can easily access their supplies. Also, if you can get a syringe or turkey baster, you can use that to get poop out of the cups without water changes. I also had their tank theomoters with them so I knew how cold/hot it was. I think I only feed them in hotel stops so they only got fed 3 times in 10 days. Or maybe I fed them 1 pellet a day. I don't remember.
Is it really important that they get out and have swim time? Even if they are in a slightly bigger jar than their cups (mason jar-ish)?
I had their stuff in a 2 gallon storage container, so I let them each have like 1.5 hours at each hotel to swim free. I don't think it's necessary though.
Also, you will be on paved roads, I was on the Alaska Highways for like a week - which was nothing but snow and ice for like 2000 miles. VERY bumpy. I'm sure they did not like the sloshing around, but they survived. I don;t think it would be much different them shipping them via plane with turbulance and whatnot.
The biggest concerns would be:
2) water quality
water changes are easy at hotels but keeping the temp good for them might be a challenge. Even in the backseat it can get too hot or too cold.
Tikibirds : I read some of your story when I did a search on these forums on this subject. So sad!
I was very sad when I found most were frozen :(. However, I was able to save some here from pretty dire conditions since I had the extra space and that made me happy. I just wish my fav guy had survived :(