Newbie....need advice on TC selection

I guess it depends, but older kids wouldn't mind a tent of their own. I can easily sleep 4 if we are talking smaller kids. I'd use my bunk over my dinette for a 5th. You don't need to go long, but you need a floor plan that works for how you will use it.

Assuming good weather for boating, I don't think you'll be inside much. Almost any TC will work for cooking, dressing, etc.