I agree on going up in 'persons per tent'. I use a REI two person as single person tent.

It doesn't sound like your going to use this on backpacking trips so it wouldn't be packed on your back. I believe Coleman makes a family type tent that holds 5-7 people. I went on a overnight to Mt. Lemmon in Tucson and five of my adult buddies slept in one. I slept in a Eagle Nest Hammock outdoors.

I may do an overnight in January climbing over the Superstitions. (Not a hard climb, or long, just a two day deal). Because it rarely rains in Phoenix my only concern is cold. Most likely to keep pack weight down I will carry a GI poncho (old school vinyl not the ripstop) as a ground cloth bivy and then sleep in my Big Anges Yampa (rated 40*). The poncho will get me a couple extra degrees as its wind/water proof and clothing options will get the rest. Figure I can get down to a 25* bag that way and save 2 pounds less tent weight.

Worst case, I can move into the tent the father/son team will carry.