How many people can join a group order?

You decide, and it is a real setting rather than a vague limit: Settings → Group orders, "How many people, including the organiser" — anywhere from 2 to 50, and 20 unless you change it. The same screen sets how long a shared cart stays open in hours, who earns the loyalty stamps, and whether the organiser may remove somebody else's item. Whatever you pick, the kitchen ticket itemises per person, so a table of twelve arrives readable.