Son in laws

This may seem trivial but not to me.

I have two daughters , younger one in a second marriage . Her first husband first came to my home when he was seventeen, now in his forties. We have a very close bond , suppose he is the son I never had and I could not care more if he had been my son. What does one call a son in law who is no longer a son in law? I have kept to my son in law but recently this has caused confusion, I was arranging for a parcel to be collected and said to the woman - my son in law or his wife will collect it !

Have requested a move of house and was asked for name of family in the area - my son in law who isn't my son in law sounds most odd. He isn't a friend , much closer than a friend , he is part of my family.