Yellowstone itself is enormous. There will be a lot of car time for a family of 7. On the other hand, it is worth it, both for the landscape/features, but also for the wildlife. We were unable to use our TT, long story involving a blown head gasket, so rented a car and stayed in hotels/camping cabins in West Yellowstone, at Grant's in the park, and at the ranch between Yellowstone and Tetons. You cannot see everything in one trip to Yellowstone, unless perhaps you spend an entire season there. At the same time, what ever you choose to do, you will have lots to see.