A.W.
My husband and I recently did the same cross-country trek down to SA from Michigan while I was 6 mo preggo, with 2 cats, a 16-ft moving van, 5 people and 2 cars. Here's what we did:
Re cars:
We hooked one of the cars onto the back of the moving truck, which was great, especially since the other car died halfway there (Missouri - during the heat wave last summer!)
Re cats:
Put them both in a large carrier. Had small food bowl for them and froze some water in a tupperware container for water. My cats did not really eat or drink while we were on the road (~8 hours/day) We didn't provide the cats with a litter box in the car, we just set one up each night at the hotel - cats will hold "it" in for a very long time. My cats are EXTREMELY vocal, but honestly, after about the first 15 minutes, they calmed down and slept. We did mostly drive-thru food until we got to the next hotel and then deposited the cats and went out to a sit-down dinner. I highly recommend investing in cat collars/harnesses with tags identifying the cats and your cell phone # on them.
That's all I can think of for now. Let me know if you have any more questions - like I said, I just did this less than a year ago.