Thanks for the info. We'll also be in St. Thomas. There are 11 of us so that might work out well!
Several important things, if you do the Baths. As the above poster said, go on a trip where your boat pulls up to the Baths, not the ones where you take a bus from Spanish Town to the top of the Baths & then have to climb down.
Also the boats like Pirates Penny can't pick up in Tortola. A Baths trip is also out for that boat from St Thomas, you don't have enough time in port.
For the group of 11, these boats would be perfect for a private charter on your day in St Thomas. They take a max of 12 people. They'll tailor the day around what you want to do & work with the cruise ship times. I'd suggest going to Jost Van Dyke, a snorkeling stop, & lunch at Willy T's, if all that is possible. Call them for info well in advance. All drinks are included in their trips & they normally serve some fruit & so forth in the AM. They are really good.
As for the Baths, you all have better port times in Tortola so should try to find a boat that departs from there. No need to clear customs either, I think. I'd check trip advisor for boat reviews. BTW, reviews on the Pirates Penny are fantastic.
As for the 1 poster, who didn't like the Baths, he might not like the Grand Canyon either.