I see that in the 1881 census, there's a household in Blantyre containing William Raeburn, 28; wife Margaret, 27; daughters Helen, Jane and Jessie; brother-in-law William Nelson, 21 and sister-in-law sister-in-law Helen Nelson, 16.
These siblings are a match for the family of Robert Neilson and Helen Duncan
Janet, 4 November 1855, Cambusnethan
Walter, 14 December 1857, Bothwell
William, 1 January 1860, Cambusnethan
James Duncan, 24 January 1862, Cambusnethan
Robert, 3 January 1864, Rutherglen, died 1865
Helen, 5 February 1866, Rutherglen
Robert, born 17 April 1869, Rutherglen, died 1870
Take a look at Janet's birth certificate. It will tell you, among other things, how many children Robert N and Helen D had had before the start of civil registration in 1855. It will also tell you where Robert and Helen were born and how old they were.
The 1871 census lists in Rutherglen Robert Neilson, widower, 38 and children Janet, Walter, William, James and Helen.
The 1861 lists Robert Neilson, 30; wife Helen, 26; and children Margaret, 7, Janet, 5; Walter, 3 and William, 1.
Helen Neilson or Duncan, 34, died in Rutherglen in 1870, mother's maiden surname Sommerville.
Robert Neilson, mother's surname Forsyth, died in Blantyre in 1901 aged 72. He may or may not be Margaret's father; his death certificate will clarify that.
In 1911 Margaret Raeburn, 57, is in a household in Glasgow Bridgeton with Jeanie Raeburn, 25, and in 1921 she is in a household with Adam Raeburn, 37.