I remember and knew several Shadowens families who lived in and around DeBerry. I don't remember your grandparents'names. Also, I don't remember being related to any of them. I really don't know enough about the subject to give you a firm answer. Jim worked very hard to develop his style of music. I was around him off and on from childhood until his death. He was fun to be around, and could he ever sing! Thanks for writing--sorry I'm no help.
Great country music is a Reeves family tradition.