I have found this information and also a reference to Frank and Jesse calling themselves the Williams brothers wehn they were together.

James brother Uncle John R James:

John R James was born in Logan, Kentucky 5 FEB 1815. John died 25 OCT 1887 at 72 years of age. He married twice. He married Amanda Polly Williams 1 SEP 1836. Amanda was born 28 JUN 1817. Amanda died 15 MAR 1871 at 53 years of age. He married Emily Bradley 1872.