On the one hand, I can see the owner's point. If it truly was discussed during the pre-employement interview and the captain elected to ignore the instructions of the owner, then the captain is at fault. Remember, who owns the boat and writes the checks. It's his boat.
If the captain had full autonomy to hire and fire crew, then it was within his authority to purvey additional watchstanders for an extensive transit from Florida to the Caribbean. I have in fact hired my father and my brother to work for me, temporarily, for transits to the Panama Canal and to Guam. Of course, I had informed the owner of the addition and reason.
What seems to me here was a either a disrespect for the owner's wishes or a complete breakdown in the owner/captain relationship. Communication, therefore, is paramount to affect a professional, and respected relationship.