It lists her parents as Hiram Devault and Lavina Beck. While you are at it look for the death certificates of their children. Sometimes they indicate where the parents were born other than just the state or country.
I suggest contacting a library or historical organization local to where they lived in Missouri to see if they can help you find an obituary for George. It may not have his parents' names but it might have surviving siblings and exactly where he was born. The church he was a member may have something in their records.