Hm. We're going out for dinner and drinks. (Do we know each other that well? ) You say: "How about if I invite Bob to come too? That way we could make it a party of four." I say: "I don't care. Is it okay with Sally?" You say: "Yeah. She said she wouldn't mind." I say: "Then ask Bob if he wants to come."
Oh, what was the question? Yeah, probably better to stick with "could" since you started with it.
(I'm hungry. I'm going to get a burrito.)