We rented 3 times before purchase to make sure that we like it, we did. :)
The first rental was a class C, 31 ft. one slide, then a 38 ft. class A diesel with three slides and finally a 38 ft. class A diesel with four slides. (renting is not cheap!).
During the second rental, friends rented a 37 ft. class A gas. We all went to Sedona, AZ, from CA. Had the best time as we all had our own sleeping quarters.
Back to your rental....... the kids could sleep in sleeping bags, no need to try and find a unit that can sleep 8. Depending on the SUV/Van, the kids could camp in that for the night, I'm sure they would love their own space.
To me, it seems a large class C would work as the adults would have their private spaces, two in the bedroom and two in the loft and maybe two on the fold-out sofa.
Have you thought about renting two class C's? That way, everybody would have their own sleeping quarters. You could leave the SUV/Van at home if you were not going be touring during the day and just enjoying camping at your three travels stops.
Anyway, whatever you decide you will have a blast even though it will be crowded. :)
Safe travels,
MM.