Why are you waiting to get engaged if you already know when it is going to happen? I would say "honey, we're engaged & give me the ring in December when you get here". LOL!
My husband asked my dad, but it is not necessary & I don't think he was expecting it. I think he maily asked because he wanted to know where we should go to pick out a ring! LOL! Anyways, if he does not really know them it might make it that more strange & awkward!
Congrats on the future engagement & let us know how it all turns out!