For convenience, I have grouped together the three daughters of John and Agnes along with the five children of these daughters. All 5 of these children were born out of marriage.
Helen or Ellen had a daughter named Marion Gordon b. 1877, in the 1881 census Marion is living with her Mother and Grandparents. In 1891 Marion is still living with her Granparents but her mother, Helen, is living elsewhere.
Marion married James Millroy in Castle Douglas in 1914 but she used the name Minnie Wilson.
Marion's parents were John and Agnes and her sister, Elizabeth was a witness at the wedding.
Marion's death certificate gave her name correctly.
Ellen had another daughter, Elizabeth, in 1881. On the 1891 census, Elizabeth is living with her grandparents. On the 1901 census Elizabeth is living with her Aunt Marion.
Maria's name seems to have changed to Marion Gordon by the census of 1871, this Marion had one daughter named Georgina in 1882 and another named Jessie in 1896. Georgina lived with her grandparents in 1891. In the 1901 census, Jessie was living with her mother.
Agnes was born in 1872 and she had a son James born in 1889. James lived with his grandparents in 1891, I have yet to find out where he was in 1901.