Have they asked you yet when you could start? If not, I would ask them when they plan on making a decision and having someone in place. If they ask you when you can start, tell them you need a few weeks to get things in order and have a family trip planned. Since it is a short cruise, it shouldn't be too problematic at all. Most people have to give at least two weeks notice if they have a job already and you're pretty close to that point. If they make the decision next week, you'll be in that two week window if you start as soon as you get back.
Note- I took a new job with a 17 day trip to Italy planned two months later. They had no problems with that as I let them know up front.