I agree with Caroline. Having an 8 seater allows just one parking fee ($12!)if you're all going to the parks at the same time. Having another car allows whoever wants to do something else at some point to do just so, avoiding bad feelings and frustrations, specially when there are young children in the party... they tend to have their own schedule, which can be slightly different from the adults' . The extra car also carries the luggage (or some people) back and forth the airport.
Have a great time in Florida!