What a tricksie family this is

Muir Street in Hamilton seems to be the key to them though. Not sure how much of this you already know, but in 1841, there appear to be four siblings with their families, living in Muir Street: William Calder/Cather/Coulter; Eleanor Neilson/Nelson (nee Calder/Cather/Coulter); John Calder/Cather/Coulter; and Robert Calder/Cather/Coulter.
The death registrations for Eleanor, Robert and John suggest they are all the children of
John Calder/Cather/Coulter, weaver, and
Mary Ann Maxwell. Interestingly, there is a John Calder/Cather/Coulter, widower, weaver, b. abt 1780, Co Tyrone, Ireland in Quarry St, Hamilton in 1851. Can’t easily see him in 1841, nor can I see a death in Scotland, but the variations in spelling I’ve seen for the surname make it a bit tricky to track down any of them!
From the censuses where I think I have managed to track them down, this looks to be the make up of the four families:
William Calder/Cather/Coulter b. abt 1806, Co Tyrone, Ireland d. before 1860, Lanarkshire, Scotland
m.
Mary Ann Johnston, before 1827, Ireland
- Mary Ann, abt 1827, Ireland
- John, abt 1835, Ireland
- Sarah, abt 1838, Ireland
- William, abt 1841, Lanarkshire, Scotland
- Isabella, abt 1846, Lanarkshire, Scotland
Eleanor Calder/Cather/Coulter b. abt 1808, Co Tyrone, Ireland d. 1872, Lanarkshire, Scotland
m.
William Neilson/Nelson, before 1838, Ireland
- Mary Ann, abt 1838, Ireland
- John, abt 1840, Lanarkshire, Scotland
- Eleanor, abt 1842, Lanarkshire, Scotland
- William, abt 1846, Lanarkshire, Scotland
John Calder/Cather/Coulter b. abt 1811, Co Tyrone, Ireland d. 1870, Lanarkshire, Scotland
m.
Mary Stewart, before 1832, Ireland
- James, abt 1832, Ireland (d. before 1855)
- Mary Jane, abt 1834, Ireland
- Ann, abt 1838, Ireland
- Jacob, abt 1840, Ireland
- John, abt 1842, Lanarkshire, Scotland
- Isabella, abt 1845, Lanarkshire, Scotland
- Margaret, abt 1847, Lanarkshire, Scotland
- Helen, abt 1850, Lanarkshire, Scotland
- James, abt 1855, Lanarkshire, Scotland
Robert Calder/Cather/Coulter b. Abt 1816, Co Tyrone, Ireland d. 1888, Lanarkshire, Scotland
m. (1)
Margaret Johnston, before 1840, Ireland. b. abt 1821, Ireland; d. before 1845, Lanarkshire, Scotland (his death record actually says ‘Mary Ann Johnston’ for his first wife, but I think this may have been an error - the death was registered by his eldest daughter by his second wife, Mary Ann)
- John, abt 1840, Ireland
m. (2)
Elizabeth Clyde, 1845, Lanarkshire, Scotland
- Mary Ann, abt 1849, Lanarkshire, Scotland
- James, abt 1853, Lanarkshire, Scotland
- William, 1857, Dalziel, Lanarkshire, Scotland
- Isabella, 1859, Hamilton, Lanarkshire, Scotland
- Elizabeth, 1861, Hamilton, Lanarkshire, Scotland
- Robert, 1864, Hamilton, Lanarkshire, Scotland
- Margaret, 1870, Hamilton, Lanarkshire, Scotland
Back to the question of what happened to William's daughter Isabella. No joy really - there is an Isabella Calder/Cather of the correct age who married a James Burns in 1863 in Hamilton. She married again in 1880 to James Lindsay. I think, however, that she is most likely the daughter of John Calder and Mary Stewart - having a look at either of the marriage records will confirm this.
Ruth