We've fit 7 (2-4 kids, 3-5 adults) into a minivan. In your config, we had 2 carseats in the middle row, a booster and 2 adults in the back, and 2 adults up front. I wouldn't want to do that for the whole trip, particularly since luggage space would be extremely scarce. My recommendation would be to go with 2 sedans (or station wagons, if you're lucky). On a recent family reunion, my and my sister's family had considered renting a passenger or mini van, but decided to go with 2 sedans. It was about the same or lower cost and afforded more flexibility as we could split up and take our own side trips.