Originally Posted by SchrodingersCat
My question is, why is it YOUR responsibility to communicate your girlfriend's lifestyle to her father? It sounds like the girlfriend and wife initiated all of this, and you're still working out your own feelings about the whole thing.
So in my mind, it makes more sense to defer explanations to the girlfriend and wife. If the daughter explains to her father that this is her decision and she's happy with it, then he'll have no leg to stand on. If the father confronts you about it, just say "Your daughter and my wife want this and I'm still processing my feelings. I would feel more comfortable if you asked them those questions." That makes it crystal clear that you're not forcing this only daughter into some kind of harem.
This suggestion is one of the best yet and since reading it I have spoken with the wife and girlfriend. We've decided we're all going to sit down together when he arrives, she'll say her thing and then if he has any questions for the rest of us we'll all talk it over with him together. I hadn't really even wondered why I was going to be the one doing the talking so kudos to you for the suggestion and thank you.
I appreciate you all taking your time to put in your two cents. Thank you for the valuable input.