Most Cruise companies should cope with that but best to check prior to booking and make sure it is noted on your booking .P&O certainly do it i think RCI and Celebrity wil.
Most cruise lines cater for special diets. You need to specify your requirements when booking.
Most cruise lines will provide glutin free product on their ships. Some will not guarantee it, because they fear being sued but you must check with the cruise lines before you book and be sure to note it when filling out the forms....Nei.
It helps if you let us know what cruiseline you are talking about. It is also nice to end a question with the word 'please'.