My ggrandfather, Martin McDonough, was born in Tiernee,Lettermore in 1852. He died after 1901 in Ireland. Martin married Barbara Toole (1853-1902), Martin and Barbara had 7 children. Their daughter Mary was my grandmother. Their daughter Bridget was the mother of Barbara Mullen.
According to Martin's birth certificate, my Martin's father was Patrick McDonough, born abt.1830 in Trabaun, Kilannin, Lettermore. I do not know Patrick's wife's name yet. I don't know if Patrick's middle name was John.
I Believe that your family connection is definitely through Patrick McDonough's children. Possibly their daughter Bridget(b. 1858?) married Patrick Sullivan in 1884. That would make them cousins to the McDonough/Mullens. Helpful? Mary