Yeah, I’m in genealogy, and going back to my great-grandpa, I’m in a similar situation. He had brothers, but I don’t know their lines.

My mom didn’t marry my father, so I have her last name. My paternal last name/bloodline combination lives on through my half-brothers, but my maternal is down to two males in my generation, with a third that is uncertain as to if he’s bloodline, or another instance of a child taking the maternal name (of which I am the only one so far).