We have a guest, friend of my FI, who has been dating 2 people for a while. I'm not 100 sure the situation but I think at least 1 of them knows about the other maybe?. I'm not saying I agree with what she does, but I just don't judge because it's not my place and she's my FI's friend, not mine.
My question is how to address her invite. I know we should list SO's by name if possible, and we could get both names, but we don't care which one she brings. Is it acceptable in this case to just invite her with a 1?