I think I have seen some on this class ship that hold 12 but 13.....that's pushing it. They 'may' be able to accomodate you once onboard so I suggest you talk to the maitre D' when you get onboard.
You may want to consider large tables next to each other, you can even switch tables/seats nightly so everyone can get together. I'd mention it to your travel agent first and if you don't get what you want, talk to the Matre'd once you are onboard. Just ask where he'l be that first day.