If your husband has a dark suit, he will be fine. You see fewer and fewer men in a tux these days. I wear one, but that's my preference. If you cruise infrequently, don't bother to buy one, and $90 to rent one is pretty steep. What Donna says about the boys attire is spot on.
Serenade of the Seas b2b January 2016
Serenade of the Seas b2b January 2017