I drove from northern Colorado to San Diego with my two kittens a few months ago.
I had a passenger, so I felt comfortable with my cats out of their carriers. I couldn't strap the carriers in, anyways, so it wasn't any less safe. I had both cats on harnesses, so they were easy to grab, and could be leashed when we had the doors open. I had a carrier for both of them, where they started out, and their favorite litterbox.
Bella just hates being in the car. She really hated the altitude changes, and she is a bit unnerved by the landscape changing so quickly. She cried a bit, and needed lots of snuggles. Rowan was pretty calm. After wandering around in the car, and sniffing things, he went to sleep in Bella's carrier. After he woke up, he moved to the litterbox, and slept there for most of the trip. I thought it was weird, but he was really calm, so I didn't move him. Rowan ate and drank, and used the litterbox, but Bella was too stressed to. I think she might have had some water when we stopped for a while, but it was a very trying ordeal for a kitten who hates to drive the 4 minutes to the vet.
The harnesses were great, it helped me drag Bella out from under the clutch, and keep her away from it in the future. I probably would have had her on a leash if she hadn't been asleep in all of the urban areas. She got a bit restless in the middle of nowhere in Utah. She slept a lot by the heels of my feet, and in Rowan's carrier. I also had their information on their collars, with my phone number and their rabies tags, since we were crossing state lines and I didn't want to be hassled if I got stopped at one of those ports of entry thingies. I also had their papers from the vet at the top of my pile of stuff.
The cats tended to already be in one carrier or the other when we stopped, so we just shut the carriers and left the windows cracked when we had to stop for food or the restroom. Once, Rowan was in the litterbox, but he wasn't even thinking about moving.
You said that you're moving with your husband, but if you're taking separate cars, I really wouldn't recommend letting the cats run around loose. I know that I couldn't have controlled them on my own.
Some people recommend test drives to get the cats used to the car, but I've found that cats either ride well, or they don't. Rowan is actually the first cat I've ever had who enjoys travelling. On short trips, he'll stand up on a seat and look out the window.
Edit: I didn't use tranquelizers (that looks like it's spelled wrong...). The kittens were growing so fast, it would have been impossible to work out the proper dose ahead of time, and they can make cats go nuts. It just didn't seem like it was worth the risk.