Pick a large ship like encore orbliss plenty to do and teens love it. Also will make new friends no need to do expensive excursions just grab a cab and head for the beach. If st Lucia is on your schedule
Look at cosol tours , private tour and cheaper than ship did 3 times worth money they may give you a price break since 6 people. Always get you back in time includes drinks and lunch and snacks. St Thomas go to secret harbor good snorkeling no charge for beach.