One thing to consider is how often the 4 of you will be in it together? If you will be using it mostly by yourself or with one of your boys then what about a 16 tandem kayak?
Native Watercraft makes a 16ft tandem with what they call first class seating, the best seat in the business. The seat is removable and can also be used on land which works out great on camping trips.
This is a kayak/canoe hybrid, it is open like a canoe with a kayak profile. I have an ultimate 14.5 and love it. It is also much more stable than a canoe.