Sounds like you should have a wonderful family reunion/party on board the Fantasy. Carnival has a great kids' program featuring lots of family activities as well as those for kids and teens only. (See section on Carnival Cruises in the article on CruiseMates.com's family site about Kids Facilities by Cruise Line. Also, I wrote a detailed review of the Carnival youth program which should be on this site any day now too.)
There will be plenty of entertainment options for all tastes on the ship as well as dancing, etc. The only people who may not get what they want are those looking for quiet spaces -- that's a little tougher to find on a Carnival cruise.
Hope this helps!
Luisa Frey Gaynor
CruiseMates.com Family Cruise Editor