Also, if you are using cages, you could combine litters in shoe boxes with hay in one cage ... compartmentalizing them. The older kits will probably all gather in one large box, but the >2 week old kits can be kept in shoe boxes with lids ... just punch plenty air holes.
As for the length of the trip ... 8 hours is not too long for adults to go without water or food as long as they have hay to nibble on. I have found that during travel, most rabbits won't eat or drink while the car is moving. Then, when they get to their destination, if there is a larger pen for them to "stretch their legs" in and be able to run around a bit, they will generally empty their bladders and seem to be a pooping pez LOL
When I bring rabbits in from a long road trip, I also only give pellets and oats for 5 minutes ... whatever they eat is all they get until morning when they go back on their regular feed schedule. Of course, they have all the hay they want. This seems to help get their gut back in motion and prevents intestinal upset.
For the weanlings, I would suggest oats with just a bit of pellets and plenty of hay, then another feeding of pellets 3-4 hours later to get them through the night. They will be hungry hippos in the morning so first feeding should be more oats and hay than pellets with a steadily increasing portion of pellets through the day. The weanlings will probably be the most at risk for intestinal upset of all. Also, if they are used to fresh fodder, you could include that each feeding.