this is one place you can read about the man himself. Mary did marry, but in SC. Her husband, also a lawyer, was a Confederate Veterans, and like his Father-in-law also served in Congress. If I can find this info on the web again I will forward it to you.
I wonder if he is a cousin to my Danial McDuffie born in NC around 1850, his mother was named Sarah born in Scottland around 1783, no death date on either of these.