I believe that your great-grand-parents were Arthur Ducharme, born around 1871 in or around Contrecoeur (Québec), and his wife Ernestine Charron. They were married on Feb 13, 1899, in Ware, acording to Massachusetts Marriage Index.
Arthur was the son of Isidore Charron-dit-Ducharme and Malvina Pelletier, married on Sep. 8, 1868 in Ste-Trinité Church, Contrecoeur(Your conjecture was good, indeed). Ernestinee was the daughter of Edmond Charron and Sophie Leblanc.
So welcome in the Charron-Ducharme family, to whom both Muriel and I belong.
I would like to know more about Arthur's descendant. Please email at my personal address so we can exchange faster.