B Gaylen, you're question is much to vague for a decent answer. There are so many different options in itinerary that selecting one without knowing what your kids are interested in would be a shot in the dark.
What do your kids like to do? Do they like a lot of activity? Do they like to snorkel? Do they like to rock climb? Do they like to be with other kids? Are they adventurous?
Give us a little more details and I'm sure somebody on this board will be able to help.
There aren't a great many ships that sail the Caribbean in August as that's the heighth of the hurricane season. Of those available, it would probably be best to take the Southern Caribbean cruises. The ages of your children aren't as important as where you would want to cruise at this time of the year. By the way, the hurricane season runs from June 1 till November 30, but the highest times are August and September.
Would suggest you go to a travel agent and pick up the brochures for the Caribbean for the various lines that sail there. You don't have to book with them if you find a better deal but the brochures will help you in your decision making ... and they'll show what's available for teen agers.
I cruise the Emerald Princess, Eastern Caribbean on April 16, 2012