I'm suspicious about "tracing songs back through the family" unless there's a contemporaneous record.

Only academic types pay much attention to just which forebear sang a song. If it's claimed to go back beyond grandma (assuming today's singer really learned it from her), and there's no documentary evidence (and there almost never is), it's pretty untrustworthy.

It's just too easy for people to assume that songs, stories, sayings, and so on are much older than they are.