Caribbean Cruise as Permanent Resident without Passport

Hi,

I have some family who would like to join me for a cruise (I am a U.S. citizen). However, they do not have a passport but rather a permanent resident card as well as U.S. drivers license (which means that while they are legal to be in the U.S. they are currently unable to travel outside the country).

I've done some research online that suggests that for closed-loop cruises they may be ok with a Permanent Resident card and drivers license, but I'd like to see if anyone on here has personal experience with this.

We are planning on departing from FLL to Cozumel, Belize City, Roatan and Grand Cayman.

Thank you for any insight.