Assuming that there is a cabin in the same or better category this is just not reasonable, you have 2 max people in a cabin capable of holding 3/4 passengers, if you owned this business would you want to lose the revenue because of this?
From a business and even practical standpoint, Princess should and does have the right to move the 2, to a like or better cabin, in order to fulfill the 3 or 4 passengers also looking for the same cabin type.