Hello Kallcoat and welcome to Rootschat.
The wife's maiden surname is really important to searching cemetery and other records but, I do think I have found your gt-grandfather and his family.
From the records of the Private Walled Burial Ground at Cambusnethan. (Situated between the old churchyard and the municipal cemetery).
I don't have a photograph of the headstone (if one ever existed) but here are the entries from the gravediggers Day Book, for plot 476 in the "Private".
All dates are of interment, so the death would have occurred a few days previously.
JEANIE PENDER, housewife, Cambusnethan, aged 20 years, married.
Parents - William Ross & Elizabeth Percival.
Interred in 476 on 8th December 1873.
WILLIAM PENDER, Cambusnethan, aged 2 months.
Parents - John Pender & Jeanie Ross.
476 on 1st January 1874.
JOHN PENDER, coal miner, Hamilton, aged 25 years, married.
Parents - William Pender & Elizabeth Dunbar.
476 on 7th December 1877.
What a very unfortunate family and December was a very unlucky month for them!
I wonder if John was involved in a mining accident? His name doesn't appear on the 1877 list on the Scottish Mining website.
Do you have a date of death for Elizabeth Dunbar? There is an Elizabeth Pender aged 71 years who died 1888, interred in the old churchyard in a family plot owned by a family named Allerdyce. Perhaps a married daughter?
Pender isn't a common name in these registers, no sign of William pre-1861.
It looks as if they were new to the parish, according to the 1851 census index William was born in Dumfriesshire, Elizabeth in Kilsyth and a son Alexander aged 13 years, also in Kilsyth.
If William did die before 1861 and is buried in Cambusnethan he will be in the old churchyard. Unfortunately, there doesn't seem to be a headstone which has survived and there are no written records for the churchyard prior to about 1875, apart from the monumental inscriptions.
Percival is a very unusual name in this area, there are records for children of Hugh Percival & Mary Steel and also for Hugh Hamilton & Marion Percival.
Hope this has helped a little?
Good luck with your research,
Lodger