You can book connecting rooms in a cat 10. ( yes they would be guaranteed. Feel free to ask more ? If needed. Chris
PS . You didn't say if you were using points. I'm playing around with points for the member cruise. It's afew points cheaper for cat 8 and cat 11 than 2 cat 10's. We are also a family of 5. Me,DH,DS-13,DS-10,& DS-6 Hope this helps