OMG I am dreading taking my two cats from Texas to Ohio in a few weeks. Lordy. They scream and growl all the way to the vet and back so I can just imagine the fun I am in for.
When we moved to France Paul and the children flew. My brother in law and me drove with 2 cats. That was a 20 hour drive plus the channel tunnel. After the first few hours the cats quieted down. It was about 4 hours with ours. I hope yours settle down sooner.
We had them in separate cat carriers to save on the fighting