The cruise ship fishing trips tend to be more like boat rides. I have done a few of them. They are overpriced usually. I don't think any commercial charter boats can get into half moon. You are stuck with Carnivals trip there.
I did Princess in Grand Turk. Carnival and Princess probably use the same company as Carnival owns Princess. See my report. Your short visit there makes it hard to get arrangements. Also the dock there is open to the sea so it ocassionally gets missed due to weather.
Grand Turk fishing trip on Princess Cruise
There are a lot of charter boats in St Thomas but you should take your wife jewelry shopping.