His Dad will be smart enough to know these questions are trying to set him up. Maybe try having a real conversation and not trying to change his mind. After all, there is a good chance you will be that Dad in the future (no matter how hard you tell yourself you won't be). Tell me how I now.
Real conversations cannot involve one or more persons trying to change another's mind?
I'm almost 50. I won't be. I have friends who are becoming grandparents now, still no interest.
I have half a century of talking with my father. If you think this is my first strategy as opposed to one that took years of therapy and personal struggle, I dunno what to tell you.
There's a wide body of social and psychological research on this stuff including multiple university departments (communication, psychology, sociology, management, teaching, etc) because "simply talking to people" doesn't actually work.