Hi Elmca, so sorry for the delay in answering, I was away for New Year.
William & Janet are buried in the old parish burial ground of Dalziel, it was the original churchyard and was still used by old Motherwell families who had plots there, up until the early 1960s.
The headstone has the following information (not necessarily in the order that it appears on the stone).
1868. Janet Hall died 20th March 1867 aged 29 years, wife of William Smillie. William Smillie died 14th October 1875 aged 38 years. His 2nd wife Jane Allen died 24th February 1903 aged 68 years.
This burial ground is situated near to Barons Haugh, at the end of Manse Road, Motherwell. The Victorians called in the Manse Burial Ground and it has recently been mistakenly called St Patrick's Burial Ground.