Welcome aboard, Katie! I'm so glad that the Disney Parks Moms Panel has been helpful as your family has planned magical vacations with Disney! It's nice to hear that you're considering a cruise with Disney now too!
While passports are preferable, guests traveling from Miami and Port Canaveral headed to the Bahamas and Caribbean do not need passports. As you can read more details about on
Disney Cruise Line's travel documents page, you'll see that adults will need a government-issued photo ID (driver's license) as well as an original or copy of birth certificate. Children under age 16 will need just the original or copy of birth certificate when traveling with their parents.
If at all possible, though, I do recommend acquiring passports for everyone in your family. We like to travel with passports as it makes us feel secure that even if an emergency arrives requiring us to miss the ship in a foreign port, we can still return home with relative ease, versus not having a passport. But, as I mentioned, it is not absolutely required, so you can certainly set sail without it.
Stop back again if you have other questions, Katie! I'm happy to help!