I would call your consulate. We received so many different answers from the cruise line, visa services and assorted websites. The cruise line told us we needed nothing, and that was completely false.
We are US citizens so your needs may be different, but were told by the consulate we only needed a single-entry visa in order to fly home from Turkey. Had we flown home from a different country, we would not need one to spend time in Turkish ports as day tourists/cruise ship passengers, ultimately leaving Turkey via the cruise ship in which we arrived. Also, we could have arranged on the ship to get the visa at the port of disembarkation, but were advised it made things smoother to obtain it prior to the trip.
Good luck to you. Have a great trip.