How about 4 small bivy tents? And add a nice light tarp (like Spooner makes)?
Even the girls could carry a one man bivy if they had too. Could use the tarp as a main comfort area with the bivys as a place for them to hold up to get out of the weather.
I'm thinking that I may just go with a four man tent, like the Eureka A Frame. It is light enough that I could carry it. And provide us with cover that we all could use. I'm not sure if the 11 year old would want to be on her own in the middle of the night. Also, keeping the creepy crawlers off all of us during the night will rank high. (Heck, I would prefer keeping the critters off me too.)