When you book, you simply book the cabana. Everything else, including getting charged more for extra guests, will be handled onboard by the Concierge team. They’re the one handling the cabanas, whether you are sailing Concierge or not. I don’t know how they’ll contact you if you are not since all our cabana bookings were done while sailing Concierge. For example, you can ask Them to split the price which ever way across multiple staterooms, in the case you are sharing the cabana.
You get the info package, including the wristbands but also the price structure, the island map, the cabana instructions and maybe a buildable paper cabana the day before CC day in your stateroom.