How can I avoid liability and be safe from law suits as a tour guide?

You should hire a lawyer to find out what licenses and insurance are required by the Bahamas. Most likely the Bahamas requires such businesses to be licensed and to be paying taxes of various sorts to the Bahamas. Also keep in mind that the Bahamas may not allow you to work there, or may not allow you to run a tourist business there. I suppose you would need a work visa from the Bahamas. Have you inquired into getting one? In most nations, even a short time of working requires a work visa. So that should be your first point of contact. Then there may also be licensing required in the U.S., since you will be getting your customers in the U.S. Depending on the state, there may be very strict requirements for a travel or tourism business. Some states require such businesses to put up a special bond, since there have been so many problems with fly-by-night tourism companies. You will really be operating a two-nation company, even for the first few trial runs. You will also need insurance. You need to check the laws of the Bahamas as well as of the U.S. states where you will be operating. Then you need to check with several really excellent insurance companies, tell them your plans, and buy insurance. You will probably want a lawyer to write up a waiver for you, but whether it will hold in the Bahamas as well as in the U.S. is so questionable. It is very difficult to make such waivers hold, especially when someone has died, been injured, gotten sick, or been left stranded. If you want to try out such work, one way to do this may be to check with existing companies in the Bahamas and see if you can get a job. Or check with one of those tour organizer companies and see if you can connect on up with them. The U.S. citizens that I have known who have run such tourism businesses have done so in U.S. states, such as Hawaii or Alaska, or in U.S. territories, such as Puerto Rico or the Virgin Islands, which are St. Thomas, St.Croix, and St. John. It may be significantly easier for a U.S. citizen to get proper licensing and insurance in the Virgin Islands than in the Bahamas.

I recommend a LLC (limited liability company). Without some sort of liability limiting entity structure you would be personally liable. Also absolutely you should have insurance!

You would be liable for everything. Not only would you need an extensive waiver from all of the participants, you would need significant liability insurance and probably a number of licenses and permits since you won't be doing this in the U.S. Talk to a number of people and companies who offer something similar about how they operate their businesses before you start your own.