Our family has only stayed on St. Thomas a few days our past 2 trips before heading to St. John so I'm not an expert but I'm happy to share what we've enjoyed and hope it helps!
We've found good snorkeling at Sapphire Beach and if you want to spend a day at a beautiful white sand beach, then it's Magen's Bay!
My husband and son went scuba diving with Red Hook Dive 1 day and really enjoyed that. While they went diving, my daughter and I went to Coral World. We did the sea trek and the sea lion encounter...highly recommend the sea lion encounter!
With 2 teens and 1 a picky eater, restaurants are sometimes a challenge...our favorite restaurant is Molly Malone's located in Red Hook. We've eaten lunch and dinner there. The food has always been good and plenty of it.
I've heard Blackbeard's Castle is a nice tour. We have that on our list for this summer as well as trying out the new zip-line course!
I'm sure others will share their favorites with you! I know you are going to have an awesome trip and have fun planning!