Gagnon-Poulin Connection

I know that Aurore (Poulin) Gilman's mother was Mary Gagnon. I'm trying to make the connection to the Gagnons that I knew when I was growing up in Salisbury MA. I think possibly Mary Gagnon and Louis Gagnon, whose wife was Rosanna, may be brother and sister but the final piece is eluding me. Can anyone help?