For an Escape VR you can't have more than 18 guests, period. They make you switch to a Wishes VR, which has a minimum expenditure of $10,000.
If you have 6-18 guests at your Escape VR, the only additional charge is for more cuvee, since the bottle that comes with the package only serves 4-6. But if you swap out the included cuvee for sparkling cider, they give you 2 bottles - which might cover all yoru guests and save you any extra fee. There is no per-person fee for more than 6 guests.
If you're talking about a Disney Cruise Line VR, you are charged a fee for more than 10 guests: