Alcoholism is also a famiy disease because genetically it means there are probably others in the family who are either alcoholics themselves and/or living with the damage of having lived with it.....maybe without even knowing it. I know that it has been very threatening to some members of my exAH's family. It really makes a mess of things for so many people,but especially the children involved. None of it is rational, as we all know.
I am having the best luck via email. My son communicates that way and usually,so do I. No guarantees but opens a door and possible way for a response in the future.
Has your son ever tried sending a message to the relatives himself, or asking his dad for the information? Just curious. May not change anything,but might seem less threatening to a paranoid brain to hear a grandson just wanted to send his Gpa a Christmas card,etc...
Good luck. Hope today is a much better day for you and glad your had some supportive friends to help you.