Someone posted a good workaround to this if the total cost is better. One person orders the prix fixe for $15 and the other orders $3 dessert. That is either $18 or $3 if guest has the free meal. Next visit, the other person orders the prix fixe and the other the dessert.
If all a couple wants is a pizza each, that is $17.00 if on Standard and paying. Just depends what you want to eat.
Also, on another thread it was reported no problem sharing the prix fixe. Could be variations among the ships as this new way launches.