I see Myrl Sanders died in St. Louis County, Minnesota on September 12, 1928. Have you looked for an obit for her - sometimes you get lucky and it will mention a marriage date.
While looking, I also discovered their son Don died in 1920. Here is the article about that. The database I used (Genealogy Bank) does not cover Duluth past about 1921.
Duluth News Tribune August 25, 1920 Page 12
Sanders,Don Darrel, 4 year old son of Mr. and Mrs. Harry Parlin Sanders 2611 West Martin Street died of accidental drowning while collecting flood wood from Saint Louis Bay August 23. Interment at Green Wood Cemetery, Superior Wis., Aug. 24