First thing to remember is hitch capacity doesn't mean the vehicle can tow that much. You can put a 10,000 pound hitch on a Toyota pickup, but you would still be limited in weight by what the truck is rated to tow. So other than making sure you have a 10,000 pound hitch, you really do need to know the CGVWR as well as the weight of the motorhome fully loaded. The CGVWR is the Combined Gross Vehicle Weight Rating. Look for the C for combined as that means the weight of the motorhome plus what is being towed. Subtract the the actual weight of the loaded motorhome (and don't forget 11 kids and 2 adults maybe be close to one ton of weight alone) from the CGVWR and the figure you get is the weight of what you can tow. You'll need to know the weight of the van.
As for having that many people in a motorhome, technically in most states everybody in a motorhome is supposed to be in seatbelts. Actually I don't know if that it most states, but I know a bunch now require it. I've never seen a regular motorhome that would come with that many seats, but you could look for a used tour bus. Those are the busses used by bands and normally contain seats a and bunks and not a lot else because they are designed to carry a lot of people.