Robin: While I know who my biological maternal grandfather was, I also am researching in depth the family of my step-grandfather, the only grandfather I knew. He was the very-kind gentle Scot who loved my grandmother and my mother deeply (and me, too), as opposed to my "real" grandfather who was, unfortunately as it turned out, a mean drunk who also was deceased before I was born. There may be no answer to your question, as others have pointed out. But the one who helped rear your mother counts for a lot in making her the person she became, as it did in my family! Best wishes, Sally