We actually just booked our first trip where it's just my husband and I (MarineMax 362) because I am tried of trying to plan with friends. They can't commit and I won't book until they're ready to pay me their full cost up front. For your friends that booked a flight home a day early, of course they can change the flight, they just don't want to pay the fees. I would tell them to pay the fees or expect it to be a rough last day or ferries and taxi cabs.