Go to the Jack county texas web site and look at the 1900 and 1920 census. I think you will find his family there. His dad came from Prentiss county, Ms. if it's the same family. Sam's dad and my ggfather were bros. I think.
Don't know anything about his wife although my gmother on my dad's side was a Johnson from Prentiss county.
There is a fellow in Ok. nameof Kenneth Gahagan knows a lot about Gahagan families. We just discovered that his dad and my gfather were 1/2 bros. Ken's gfather also mrd. a Johnson from Prentiss.
Let me know if it looks right.