I just today discovered this forum, and have read the John BARKMAN/Hannah DAVIS postings with interest as I, too, am directly descended from this couple.
My paternal grandmother was Rossie Eleen BARKMAN, b. 1 JUL 1881, Texarkana (Bowie) TX
Rossie was the daughter of Jerome Bonepart BARKMAN (1839-1892) who was one of John and Hannah's offspring.
Rossie married Walter Lee MERCER, a building contractor) in Bowie County in 1901, and, though she had at least two still births, she left seven surviving children: James Allen MERCER, Rossie Lee MERCER, Maudie May MERCER, Joe Barkman MERCER, Mary Eliaabeth MERCER, Millard MERCER, and Amber MERCER.
Both Rossie and Walter Lee (along with my father)are buried in the BARKMAN-MERCER family plot in Rose Hill Cemetary in Texarkana.
I have been unsuccessful in finding a BARKMAN link beyond John but am interested in having more information about the Jacab (Jacob) you mention - particularly anything you have concerning the Miami connection.