Looks like we were all taken in by Bennett's family history again. It looks like Fannie was really Fannie Mann. Robert DeShazo was close to Jarvis and Fannie, and the history says Mary Mann was married to Robert DeShazo. Maybe Mary Mann married DeShazo after she had given birth to Sarah and Fannie and after Boreham had died? I have no idea.
Here are court records from 1818.
Series: S165015 Year: ND00 Item: 04153 ignore: 000 Record 1 of 4 records BOREHAM, BEVERLY, AND OTHERS, PETITION ASKING TO BE GRANTED THE PROPERTY OF HIGDON BOREHAM, WILLED TO HIS ILLEGITIMATE CHILD SARAH MANN, WHICH WAS PARTIALLY ESCHEATED TO THE STATE AND PARTIALLY GRANTED TO JARVIS ASBELL, HUSBAND OF FANNY MANN, SISTER OF SARAH. (2 PAGES) View all index terms No date No online image available