On the Celebrity Galaxy, my family of 4 (I was 12, my brother was 8, at the time) shared an Oceanview cabin. My parents got the beds pushed together, and there were two fold out bunks from the wall.
We had plenty of space and never felt crowded.
But I have heard the older RCI ships have pretty small rooms. Try and find out if the Grandeur has cabins w/ the fold out bunks. They worked out really well for my family!