Hi, Nancy ...
There is no expectation that you share wine with your tablemates, particularly if they are seasoned cruisers.
Last year on Rottie VI, our table of seven all loved a small wine that was hiding in the list and did take turns buying it since we all wanted the same thing. That's unusual. We all drank about the same amount with each meal, so it was "fair". (I still think the price was a misprint on the wine list. It would have been cheap at twice the price.)
If you don't down an entire bottle at one sitting, the sommelier will happily store it for you to consume the rest another night. Wine by the glass, while convenient, is tres expensive. Better off with a bottle.
Last week on Summit, we had dinner in the Normandie with new friends. The husband and I preferred white, the wife and my husband preferred red. We ordered the two bottles and asked that the price be split evenly. That worked.
Raise a toast to CruiseMates, won't you?