My partner and I have cruised on Norweigen twice (but not on the Sky). We had no trouble spotting the other family members. As long as your gaydar is in reasonable working condition. . .
We found NCL to be very accepting of us and the other gay folks we met. We ate together, danced together, and no one ever gave us any trouble at all.
If this is your first cruise together, I think you'll be pleasantly surprised how much fun you will have in a largely non-gay environment. In my experience, cruise passengers in general seem more open-minded, and one of the reasons they cruise is to meet people from all backgrounds.
I echo the words of Ed. We were abourd the Sky last year and frankly saw more gay men and women than we had on other cruises. The staff was *very* friendly and warm ... a Friends of Dorothy meeting was also in the ship newsletter activity sheet.
I think all in all you will be pleasantly surprised.
P.S. Beds are hard on Norwegian ... please know you can ask for a foam mat. I did.