William Lilly and Mary McBride were married in Bothwell in 1864. You can view and download a copy of their marriage certificate at modest cost by going to
www.scotlandspeople.gov.uk and investing in some credits.
According to a transcription of the 1881 census the family were living in Bothwell: William Lilly, 39, ironstone miner; wife Mary, 35; Jessie, 11; Francis, 9; William, 6; Jane, 2; Robert, 3 months; father in law Francis McBride, 66, blacksmith's hammerman, born Ireland. All the rest were born in Bothwell. You can and should view the original census at Scotland's People.
Robert Lilly married Lizzie Cameron in Bellshill in 1902. You can view that marriage certificate too.
If you want to find out who the 8 or 9 children were, you can use the 1891, 1901 and 1911 censuses, which are also online at Scotland's People. The International Genealogical Index (IGI) at
www.familysearch.org lists five of them: William, 26 December 1864; Annie, 16 April 1867; Janet, 26 February 1870; Francis, 29 March 1872; William, 5 September 1874 (presumably the first William had died). You also know about Jane, born 1878/1879; Robert, born 1880/1881; and Alexander, born 1887, so that leaves you just one or two to find.
From the names of the children (first son William, second daughter Janet) you would expect William's parents to be William and Janet. In 1881 there are a William Lilly, 66, coal miner; wife Janet, 61; daughter Jeannie, 17; son William, 18; and son Adam, 3. I don't believe the last one. I also supect that the 18-year-old William is the illegitimate son of Mary Lilly, born 8 January 1863. Jeanie probably is their daughter, born 29 August 1863, parents William Lilly and Janet Stewart.
The IGI lists four children of William Lilly and Janet Stewart: James, born 12 April 1855; Barbara, born 1 April 1857; Martha, born 8 February 1860; and Jeanie. 1855 certificates are like gold dust for genealogy, because they contain far more information than any earlier or later records. James' birth certificate will tell you how many other children William and Janet had before 1855, and their ages and where they were born.
The 1851 census transcription at FreeCEN
https://www.freecen.org.uk/cgi/search.pl lists the family in Bothwell: William, 35, coal miner; Janet, 30; Adam, 15; William, 10; Mary, 8; Janet, 5; John, 9 months.
If you are looking for living descendants, that isn't quite so straightforward because you cannot view online births less than 100 years ago, marriages less than 75 years ago or deaths less than 50 years ago. If you want to see these later documents, you need to go to the Scotland's People Centre in Edinburgh, or get someone to go on your behalf.
You should follow up by viewing all the originals of these assorted documents at
www.scotlandspeople.gov.uk. Never trust anything you find online, unless it is an image of an original document, and even then be wary because mistakes can occur. And that includes everything I have said above. Check it out for yourself.