Jonathan-
Just noted you are from Durham- I used to live in Chapel Hill. The local Hobie Fleet used to be very welcoming of non-Hobies (I haven't lived there in ~6 years) and would be a good group to hook up with. You will be fine with the either of the "kids" onboard your P 16 (IMO)- I used to have one and have had up to four adults on it. Space gets a little cramped and weight distribution on the boat is something that's a little harder to control but is really only an issue in higher winds. If you are looking for a boat to handle, say, all these "persons" (2 adults, teenager and 5 year old- your family perhaps??) I would recommend an 18-20 foot boat. If you like the simplicity of the P 16 then a P 18 or Nacra 5.7 or G-cat 5.7 would be good (even a Nacra 5.0 if you want to stay 16 or the Hobie Getaway) if you are willing to deal with daggerboards then a P 18-2, P 19, Nacra 5.2, 5.5, or 5.8 or Hobie 18 (especially the Magnum since it has the "wings" that provide more spaces to "sit") or 20 could be considered.

Hope that helps some-

Kirt