I'd give the tent outside a second thought, weather permitting. Most times the kids think it's just great fun to have their own space. Obviously, age and security are primary, but you could have them inside for dinner, maybe a movie or games and then head outside. Do you have a portable DVD player? Certainly could take that or something similar to their spot and watch another movie. Family time and then their own time...not an all bad idea.
If push comes to shove, the dinette will make a decent bed. I had the honor one night and it wasn't bad. With 2 larger size kids I'd make some sort of center support, just for the added stability.
Good luck and happy camping!