I think we need to let the GM come on here and say what he wants. We've had a few people express interest but not submit characters yet so to be fair to them I think if they are still interested they should be given the opportunity to submit characters.
This is starting to look less like a family and more like a school outing so, yeah...
I'd be happy with 2 parents, 2 sons and 2 daughters myself. While adding friends is a way to get more characters in, the taboo factor is lost, so perhaps all family is the best way to go.