In my experience it will be open seating for the first night, people seated as they show up. The table you get is the table you get, shared or otherwise. If everyone doesn't show up together, oh well. Expect madness. It's a lot of people who need to be fed in random order. Hopefully some, or many, might like to enjoy dinner in San Francisco?
I imagine some exceptions will be made for Grandmothers to show up a few minutes late, but she can look at the menus ahead of time and have some idea of what to order. They (or you) could call the cabin from the MDR when a table is ready.