Elwin J Johnston

I am looking for my family's history. My great grandfather was Elwin J Johnston born 1902 in WI died 1966 in Oregon. He was married to my great grandmother Thelma A Johnston ( maiden name unknown) born in 1905 died in 1989 in Oregon. I have been told two different stories in regards to her. One that she was full blooded Cherokee Indian and the other that she was half blooded. The only other information I have been able to pull up is her death certificate number. There was a family squabble years ago with my great grandparents and my grand mother. This caused her to never talk of them. If anyone could help me with information pertaining to either one of these two people I would be very thankful. I do know that Elwin's fathers name was George W Johnston born in MN in 1869 and his mother's name was Martha or Dorthy (census records show both names with their children  listed), she was born in 1869 in England and came to the US in 1872. They had four children three living Rubin, Elwin, and Martha.

I am also looking for any aunts and uncles that I may in the Oregon area so that way our family can reconnect to each other. From what my father told me there was about 7 kids from my grandparents he believes that their names were James, Everette, Lewis, Peter (or Paul), John, Martha, and an adopted daughter named Amanda or Alice. Martha was born in 1931 and she was the youngest of the children, besides the adopted one.

Martha M Johnston Married a man named Cooper in or around 1949. Their children are Everette Eugene Cooper (born 1949 in Portland Oregon. Name later changed to William (Bill) Jacob Hendrick VanTwuyver Jr the 3rd. Was told by the man my grandmother married that he was not his son) Lewis Copper, Nancy Cooper, and Martha (Marty) Cooper. Martha married William Jacob Hendrick VanTwuyver Sr and had three children. Elisabeth, John, and Alice. Martha died February 25th 2000 in Washburn, Missouri.

Any help would be greatly appreciated.thank you