I've had plenty of fun workplace flings. However! They always happened because the female threw herself at me. Moreover I never had mother in the same office...that would probably keep me from messing with things. In a nutshell, I never asked out a coworker that I banged (didn't have to) and I certainly would never, ever ask the mom about it.
If the 19 year old goes crazy for you and her mom somehow signals her approval (not sure how this would happen) then maybe consider it. But you cannot ask out the daughter and you cannot ask the mother. In fact if you even want to simply up her interest level you have to come across as someone who wouldn't think of such a thing while still being attractive. Yes, this also means spin other plates and be obvious about it. Basically be the attractive 41 year old gentlemen with the interesting dating life. And if you do that you probably won't need any of this nonsense anyway.
Still gonna have some fun in the office with this chick. Mom and I were also tag team busting on her today. it was a blast!