Shouldn't be a problem. The big cruise lines (Royal Caribbean, Princess, Celebrity, P&O etc) tend to rig their rules so you have to buy the cruise from someone (either themselves or a Travel Agent) in your country of residence. There are ways round it, but lets forget that for the moment. If you both agree to go on, say, a Royal Carribean cruise on a certain date, you can both book independantly. If you then want to ensure you sit together for dinner, you have the option on the cruise lines website to link the reservations. (You give their reservation number and they give yours). Usually it is better to buy in your own country (but not always!) and there are rules to disuade you from doing it. You can get lots of info from thousands of cruisers at www.cruisecritic.com