As the previous poster mentioned, dinner attire for teens is the same as that for adults. Are your teens boys or girls? Girls tend to get a little dressier than boys... still, even at 14, a boy should have at least a long-sleeved button-down shirt on formal nights. The other nights, anything but shorts, T-shirts, or blue jeans are fine.
Regarding excursions, what do your kids enjoy doing? Are they content to hang out on a beach (like my 13-year-old is) or are they into something more active?