The happiest big family guy I have met is using a Ram MEGA-CAB with a snugtop canopy to tow his long trailer .
?? That's great, but it won't fit 7 passengers like the OP needs unless they're going to stick some kids in Rubbermaids.
Estimates of 1200lbs of tongue weight and 700lbs of passengers may be reasonable but it means you need a tow vehicle that has a payload rating in excess of 2000lbs. That's going to be a stretch even for 3/4 ton SUVs. A 1 ton van would be better suited. Don't forget that the kids aren't going to get any smaller either.
As for the length, sure it can be done but it won't be fun. In town driving and fuel stops are a pain and you will be much more limited on campsites available. My TT is 31' (35' overall) and as much as I love the space, I will go smaller next time. Sites here book up fast and getting one is only more difficult when I only fit on 15% of them to start with.
