Your man John Colligan is a puzzle indeed. The John Colligan who died in 1874 was, indeed, married to a Helen Gardner. He died from injuries sustained falling down the stairs at the Greyhound Inn in Sorn, Ayrshire. His death cert records him as an ‘engine keeper.’
The same Helen Gardner died in 1884 in Holytown, Lanarkshire - her death cert records her as the widow of John Colligan, ‘engine keeper at coal pit’. Her death was registered by her son-in-law, William Knox, who married one Margaret Colvin (as she is consistently recorded) in 1865 in Bothwell, Lanarkshire - on her wedding cert, her parents are John Colvin (sic), ‘engine keeper at colliery’ and Helen Gardner. This Margaret Colvin/Colligan is too young to be the Margaret Colligan born to John Colligan and Helen Gardiner in 1839 - she’s 18 on her wedding cert, so must have been born around 1847 - perhaps the earlier Margaret died?
I think I may have found Helen Coligan (sic) in 1881 in Holytown, Lanarkshire - she is a widow and green grocer - living with her is her granddaughter, Elizabeth Knox - the daughter of William Knox and Margaret Colvin (sic):
Helen Coligan, head, 68, Shotts, Lanarkshire
John Cooper, nephew, 25, Bothwell, Lanarkshire
Elisabeth Knox, grand daughter, 9, Bothwell, Lanarkshire
And possibly the family again in 1871 in Hamilton, Lanarkshire:
John Colligan, 51, Dumbartonshire (it’s been transcribed as ‘Camprie, cumberlandshire’ by Ancestry - but looking at the original, it’s almost certainly Campsie, Dumbartonshire), coal miner [his age here ties with the age of 'approx 55' given on the death cert of the John Colligan who died in Sorn in 1874)
Ellen Colligan, 58, wife, Shotts, Lanark
Jean Higgings, 41, visitor, Ireland (looks like ‘travelling draper’)
John Colligan, 16, nephew, New Monkland, Lanark
Henry, Mcdonald, 11, visitor, Rinnamill (sic), Lanark
Ellen Colligan, 5, granddaughter, Rothwell (sic) - probably Bothwell, Lanark
Haven’t yet succeeded in tracking down any of the relatives mentioned in the 1871 census entry to see if it really is the same family. And also can’t find them anywhere before 1871, using any variation of Colligan/Coligan/Coligen/Colvin… etc…
Ruth