Wes,
The Scotlandspeople site has an RC marriage for Thomas Fitsimons or Foreman to Sarah Ann Foreman in Dundee, St Andrew’s parish, on 8th May 1850.
There is a death in Cumbernauld in 1897 for a Thomas Fitzsimmons aged 73. GROS ref 495/26. That death certificate should give you his parents’ names. It should also tell you whether Sarah was alive or dead at that date. I looked for a possible death for her but did not see one.
https://www.scotlandspeople.gov.uk
I had a quick look at the indexes for the 1891 Scottish census. There’s a Thomas Fitzsimmons aged 70 in Cumbernauld with sons Patrick 27 & John 24. (I don’t see Sarah). And next door there’s a Hugh Fitzsimmons (26) with his wife Catherine. (25) and son John (4 months). I’d guess Hugh was also a son. You could investigate those, by checking earlier censuses and birth records.
They were probably in the mining industry.
It may help your search to know that Cumbernauld is in Lanarkshire, rather than Dunbartonshire.