Do you have a room or area to serve 20 people for lunch?

Yes

Yes, there is one room at the restaurant level. They also have conference rooms upstairs.

Yes. They have a private room in the restaurant that can hold that many people. In addition, there are 2 large ballrooms that can be partitioned into smaller sized rooms, as well as two smaller sized ballrooms that would also work. There are plenty of options to choose from.