I really dont know if you should or shouldnt have him to talk to your sons. But I do believe in my own opinion you should let them know that he did call even if it did take 27 years for the phone call.
I only say this because my grandfather and my dad didnt see eachother for forty years. Supposedly my grandfather tried getting into contact with my dad but my grandmother never told my dad about it. My father always felt bad about not being able to talk to him and esspecially not being able to have the choice in not talking to him. A few years back my father found his sister that he never knew he had on the internet.
I am bouncing around here Rozied I guess you just need to do whats right for you and your sons.
Jewel