We have been on 2 P&O cruises (Oceana and Auroa) as a family of 5 (2 adults, 3 kids). P&O do not allow more than 4 passengers in any room on any ship so we have had to take 2 rooms. Aurora has connecting rooms but these are high grade and therefore fairly pricey. On Oceana we took adjoining but not connecting rooms. In the booking you must put one adult in each room, but on board can sleep as you wish. Another problem on P&O is 1st 2 cabin occupants must pay the full adult fare so you end up paying for 4 adults. Obviously cheaper if you can team up with in laws or friends if they don't mind sharing with one of your kids.
Try oceanvillage, they cater for adults and children of all ages defo recomended, hope you enjo.
You either get TWO cabins, or you 'top and tail' two of the children in one bed. Each cabin has two beds and two bunk beds.
Best wishes C.T.
Unfortunately i don't think its possible .We have been on one previous cruise on ocean village 1 with 3 children and the only way for us all to go was to take the inlaws! Were doing it again on Ventura 2008 Sept same kids same inlaws.