Struggling to see William in the censuses 
Did he die in 1888 in Dalziel at the age of 55?
Was he married to an Elizabeth Mair/Main, who died also in Dalziel in 1894 at the age of 57?
I can see two children to this couple:
Joseph Pentland b. 1857 in Bothwell
William John Pentland b. 1862 in Old Monkland
Can't easily see a Scottish marriage for them either. The 1862 birth of son William John should include a date and place of marriage for parents.
Monica
Sorry I'm late with a reply, work has been crazy!
Yes, that's them. Joseph born 1857 is my great, great grandfather. I estimated his father William John's birth year from his death certificate (he died aged 55 in 1888 and I have the death certificate). But, as already pointed out, the information is only as good as the person handing it over and maybe he wasn’t 55 years old?
William John was married to Elizabeth Main/Mair and I have her death certificate for 1894.
Joseph Pentland born 1857, died 1901 married Christina Gillespie 1884 (I have the marriage certificate that give the parent’s names as William Pentland and Elizabeth Mains). I also have Joseph’s brother’s birth certificate (born 1862), but not Joseph’s (it doesn’t help that his brother was also called William John!)
I also have a 1891 census in which Joseph aged 33, Christina aged 31, William aged 6 (my great grandfather), Margaret aged 4, James aged 2 appear.
I found the Pentlands to be more elusive than other sides of my family - there never seem to be many marriage certificates or appearances in the census. My dad wonders if they didn't just adopt the name at some point!