First, if you havent already, check with the airlines and cruiseline to be sure they will let you travel at 26 weeks. Youre cutting it close with the cruise part I think, depending on the line. If you get the ok, then be sure to bring a copy of your records from your dr and phone numbers just in case.
We normally cruise over the holidays, and last year I was 3-4 mos pregnant with #2. Our son was almost 3, and my dad and brother come along too. They would watch our son from time to time, but for the most part, this is our family getaway so we try to do as much together. Occasionally, a nice dinner for two or a jump in the hot tub is nice. As for doing tours, we skipped them and just walked around port and went to a beach for a few hours. Tours are usually too long, hot, humid and boring for a little one. Give them some sand and water and theyre happy! We brought along some cheap sand toys (Target has some) for our son to use at the beach.
As for being pregnant-Im not one to get seasick (we're boaters) but I will say that I felt the motion a lot more, and it took a week to get over it once back home (landsickness). Watch your sun exposure and try to stay out of it as much as possible. You could end up with the mask of pregnancy. Wear sunscreen, drink lots of water. Avoid alcohol, greasey foods, certain fish, sushi, caffeine-same stuff as you would at home. If going to uncertain ports, avoid the water, frozen drinks, ice, peeled fruit, etc-again as most people do anyways. Watch you footing on gangplanks, stairs, etc. At that point you may not be able to see your feet! And most importantly-just take it easy and relax. Enjoy your cruise and the extra help because soon enough youll be going crazy with another child! Best of luck and congratulations!