Hello. I am researching my Coburn ancestors and I came across your query. I am also descended from this line and I would like more info on Francis. I would be happy to share what info I have. I have not been searching in Martin Co. I did not have Andrew listed as Francis' brother. I did have these names listed as his sibs: Christine, Mary, George Jr., Elizabeth, Ann, and John. I do have more info on some of these including lists of children.
Hope to hear from you,
Stephanie Coburn Hammonds