I am descended from Joseph Brotherton and Polly Duncan. p/o Margret and Susan who both married Duncans. Polly d/o John Duncan. I too question whether Margaret married this close a relative. Some even said it was John her uncle. I a certified genealogist if this was likely and was answered no. Have you checked the web site www.dsa.duncanroots.com My son just forwarded me some information off of that. A lot of info has been collected about that line of Duncan. It might also help that the abbv. for Mississippi is MS. Also Mississippi Connecting families is a good website. I can't remember exactly how much they have about the Duncans. Would love to share information with you.