Joanna, I agree with the others that you shouldn't feel like you have to be the TA for the group. You'll drive yourself crazy. I think you should let everyone book their own excursions with their own credit cards etc.
Here is the website for http://www.islandwings.com/ I agree with Denise, these excursions fill up fast so they should get on it right away. This is your vacation too....don't drive yourself nuts trying to coordinate everything for everybody. You and Tony make your own plans, let them know what you plan to do and they can decide to join you or not.