To set this up on the Medallion app, you’ll need to have everyone’s booking number. Once you have those, you will go to the tab entitled “Travel Companions” and you can add everyone there. Once added, you would go to the “Dine My Way” tab and select the time and dining room, and check all the dinners. IDK if you will be able to even select all 12. I agree with having two tables of 6 and then meeting with the dinning room staff on the first day to arrange tables next to each other.