You have to rent is through the shore excursion page. If it is not available it is probably all sold out.

Check the shore excursions page. It has renting cabana as on of the shore excursion option. However, since space is limited, the cabanas get sold out fast.

No tendering means that the ship will dock at the port. In some ports, because the port is shallow or if there are no slots open at the port, the ship has to anchor at sea and you will be tendered to ports by small boats.

Yes, we have been twice on different cruise lines and each time there have been lockers that you can use at no charge. You simply lock them up and are given a key to hold while your on your excursion.

At all ports there are plenty of shopping opportunities near the port. Depending on the ports you visit, some of them have beaches within walking distance of the port. You can always get a cab that will take you to a local beach for much cheaper rates.

The beach chairs at the beach are complimentary.

From what I was reading in the past, the reef around the Caye is protected and some of it has been damaged. The closest place where you can dive is Placencia. I don't think there is enough time to go to Placencia, catch a excursion from there and come back to the Caye.

There is no scuba diving around the Caye. The closest place where you can dive is in Placencia and there isn't enough time for you to take a ferry to Placencia, do the excursion and come back to the Caye.

Unfortunately, you likely will need to purchase a full-priced tour ticket to observe.

There is a thermostat in your stateroom which you can set to adjust the temperature in your room to your liking. The public areas of the ship will be cooled to the low 70s.