Them: Do you have room at your seder for two more?

Me: Of course.

Them: We don't want to impose.

Me: We'd love the company.

Them: Are you sure? We don't want you to have to cook extra at the last minute.

Me: "Let all who are hungry come and eat." Also, I cook on the assumption that Eliyahu and his entourage will appear at the door. It's fine.

(And if Eliyahu doesn't show up, I have food for lunch the next day.)