We did something like this in 2013 - 6 adults, but only 1 kid almost 2. Rented 2 cars, DH and I took 1 car and took DD back to the condo (near Sea World) every day for lunch/nap. My sister and her SO, and my parents, used the other car. It worked well because we were usually up much earlier than them, and got to the parks close to rope drop. My sister and whoever wanted to sleep in would come in the late AM, we'd text and meet up and do some rides together. This was in the days of the paper FPs, so my sister and SO would take our cards and get a slew of FPs while we took DD on Small World or the carousel again, and then we'd do some rides together. Some combination of the adults would stay in the park through the afternoon, while DD and at least 1 parent went back to the condo for nap. Then we'd all regroup at the park in the late afternoon for some rides, dinner, etc. and then one car would go back for early bedtime, and another car would stay later.
I much prefer staying on site, but this was totally workable since we also saved a lot of $ (ate most meals at the condo) and had a lot of space.
