Let me get this right.
A large family books a cruise and fails to show up due to an unfornuate accident. And you want compensation from NCL for a future cruise.
Was NCL at fault?
Did you purchase Travel Insurance that would have covered your lost fares?
Next time I highly suggest you buy Travel Insurance. This is why they exist.
NCL probably lost money because your family failed to show up. While they didn't have to feed your family, they still bought the food to feed them. Your family didn't spend any money at the casino, at the specialty restaurants, at the photo center, for shore excursions, for drinks, etc.
I'm sorry your family had an accident on the way to your cruise, but it wasn't NCL's fault.