I think putting the two boys, (Owen and Aidan) in the basement would be good. As kids, they'll find it pretty cool having their own space from everyone else. It could be like a little hangout for them, but they'd still have their own rooms. My 3 girls, (Skyler, Willow and Lexi) can have 3 rooms upstairs. That way, Mark and I can have our own room, and still have extra space downstairs on the main level for other things, such as a computer room.
What do you think of that plan?

sounds like a good plan. Is your entire basement those two rooms? or is it two rooms and extra space?

I think sharing a room is ideal for young children, my neighbor with qunints conferted her basement into a super baby room and than she'd sleep down there as well with the babies.