I would recommend seeing who gets contacted first (that is the hard part so don't make it more difficult). Do not mention your 'better halfs' until you get interviewed and they actually are asking questions about availability, etc. Make them really want you first.
When it comes to cabins you should PLAY UP the fact that you want to share a cabin. That frees up another cabin for another staff member - something that could be a bonus.
But not being willing to work separately is a MAJOR problem to the cruise lines. They need flexible people they can move to different ships when they need them. At the very least one of you would probably have to start before the other, possibly by a few months.
Frankly, I don't think your approach is going to work. There are a lot of veterans on ships who want to sail with their spouses. Cruise lines usually hold that out as a reward for a long time in service. Giving that to you two immediately would upset the whole reward system for the existing crew.
You have nothing to lose, but basically, your only chance is to luck out and find a cruise line that needs both positions filled on the same ship at the same time, and that is pretty unlikely.
You have nothing to lose by trying, but don't get your hopes too high.