What is the most people you can have for a birthday dinner ??

there's no limit, but you should call in advance so they can plan and make arrangements ;)

I believe you can have as many as you wish. They have Party Menus (according to diff) party themes And A Party Page. If you're planning on having a really big birthday dinner and are worried, just give them a quick call first and let them know how many ppl you are wanting to have.

I have seen party of 20

I don't think they have a limit.