My kids are practically the same age as yours and we were fine in a cat. 4. The only bad thing was the murphy bed coming down in front of the veranda door - my daughter is the last to rise in the morning and I had to climb over her to get outside to enjoy the view. Yeah, its cozy, and there was one backpack that was always in the way but it was ...nice. Like sleeping in the living room or something. The split bathrooms worked great. My oldest, who was almost 11, was out of the room a lot - we would all be in bed when he got back at midnight from his clubs. Mr. Independent. But usually during the day, there were only two or three of us in the room at one time.
If you're into a lot of privacy, it might get sticky, but there is a curtain to draw in the middle of the room for changing etc. My guys are not known for their modesty. If you can afford and really want the extra space, go for the Cat 3 but the Cat four is plenty.