I have only recently started looking into my family history and came across your message whilst looking for children of William Aitken and Helen McNish. It would appear that we are related through William Aitken.
William a coal miner from Harthill had 6 children with Helen whom he had married on 21-Sept-1866. He also had an illegitimate child called Minne from a relationship with Elizabeth Watt (I cannot trace Elizabeth at present). Although I have a death register entry for Minnie, she tragically died aged 19.
William and Helen's children were;
Joseph Aitken 1867-1943 (my great great grandfather) William Aitken 1869- Robert Aitken 1873- (your great great grandfather) Mary Aitken 1871- Helen Aitken 1875- Elizabeth Aitken 1880-
I hope this is of intrest to you, I will be visiting Harthill in Febuary just to see where the family lived.