I have taken our 4 on a 12-13 hr drive before. It's not a lot of fun for anybody. The little bunnies are fine, they just snuggle together and nap. Tony is the same, but he shares a carrier with Muffin, who digs digs digs. She hates it--she'll tear up the newspaper in the cage, kick litter all over, and throw things. Try taking your bunnies on a test trip around town to see how much it stresses them out before you decide. Muffin will dig, whether it's a 12 hour drive or a 20 min drive. Last time we went to visit the bf's family, we boarded the bunnies at the vet. For around $30 a day (split two ways), it was worth it to not have to go through the stress of 4 bunnies, a hamster, and 2 people in a car for 12 hours, plus taking care of them all while we were on vacation at a house that already has 2 dogs and a cat as permanent residents.
Most important: have a small carrier--have just enough room for them to flop if they want to. Smaller=feel more secure. Have a water bottle and make sure it won't leak everywhere, getting bunnies and litter and hay wet. Make sure you hang it somewhere where the bunny won't sit on the spigot the whole trip and get soaked. Put down newspaper and bedding (litterbox stuff) in the carrier, and then put hay on top. This doubles as a travel litterbox. Change it before the return trip. Give them a few minutes in the carrier to acclimate before you start the car trip. Don't feed them that day until they're in the carrier--it makes them more comfy in there if they've eaten, and they will eat because they are hungry. When you arrive, give them time in their guest room alone to acclimate, and give them new food.
edit: Another option is to put down a towel in the carrier with hay on it. Also, make sure that you can stop and pet them, speaking soothingly, if they get scared and need reassurance. When we travel, that's the responsibility of the co-pilot so that we don't have to stop the car whenever Muffin starts thumping and digging.