If you don't have a huge amoung of luggage, and it doesn't sound like you do, a Ford Explorer (or similar) would work; yes, someone would have to sit in the middle, but I think it would be a reasonable option and save money on the rental and on the fuel. Other vehicles I've seen in this category are the Nissan Armada and Chevy Tahoe.

I had a Chevy Suburban this week on a rental from SFO. This would easily have held your party and all your luggage, but would also be a large investment in fuel and in the rental itself as the difference between a regular SUV and a large SUV is significant. This is in the same category as the Ford Expedition and could be substituted -- there are a number of vehicles you could recieve instead of the expedition but they would all hold your party.

There are pros and cons to renting in SF rather than at SFO. There are *many* more vehicles available at SFO, so you could probably switch to something else much more easily. In SF, you are much more likely to be stuck with whatever they have available. That said, you won' be paying the airport fees so that should help save money.