You must get in touch with the cruise line who may require you to liaise with their medical advisors/Doctor on board. It should be in the brochure what you should do and who you need to contact. Either that or speak to a cruise specialist (one of the big companies on the internet) who will be able to advise on cruise lines who may cater for these allergies. You must declare it to the cruise line and also to the insurance company that is covering those members in your travelling party. All cruiselines REQUIRE one to have insurance and ALL insurance companies require one to make a declaration of any medical conditions, tablets taken, allergies etc. they will usually cover though sometimes there is a small extra charge. I advise you strongly to ensure that all is in order for all the party before you leave as the costs involved in any medical emergancy can be enourmous.