1841 Census says James Jack's occupation was a Carter. On Margaret's marriage to Leslie Rankin, her father's occupation is a Steward. So, could James Jack be working on a farm as a Carter, then by Margaret's marriage in 1848 he becomes a Farm Steward?
This looks as though it could be them
Marriage date: 29 Jan 1819 Barony, Lanark
James Jack & Ann Bowman
1841 Census: Robertson Lane, Lanark, Lanarkshire
James Jack, 46, Carter
Ann Jack, 35
Margaret Jack, 19
Ann Jack, 15
James Jack, 10
Jean Jack, 7
Cecily Jack, 5
Janet Jack, 3
(All born Lanarkshire)
Found on Family Search web site
https://www.familysearch.org/Marion Jack
Event Type: Birth
Event Date: 21 Oct 1819
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original): Glasgow, Lanark, Scotland
Gender: Female
Father's Name: James Jack
Mother's Name: Ann Bowman
Margaret Jack
Event Type: Christening
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original): Glasgow, Lanark, Scotland
Gender: Female
Birth Date: 14 Sep 1821
Birthplace: Glasgow, Lanark, Scotland
Father's Name: James Jack
Mother's Name: Ann Bowman
Thomas Jack
Event Type: Christening
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original): Glasgow, Lanark, Scotland
Gender: Male
Birth Date: 23 Aug 1824
Birthplace: Glasgow, Lanark, Scotland
Father's Name: James Jack
Mother's Name: Ann Bowman
Ann Jack
Event Type: Birth
Event Date: 2 Jul 1826
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original):
Glasgow, Lanark, Scotland
Gender: Female
Father's Name: James Jack
Mother's Name: Ann Bowman
James Jack
Event Type: Christening
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original): Glasgow, Lanark, Scotland
Gender: Male
Birth Date: 20 Dec 1830
Birthplace: Glasgow, Lanark, Scotland
Father's Name: James Jack
Mother's Name: Ann Bowman
Jean Jack
Event Type: Christening
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original): Glasgow, Lanark, Scotland
Gender: Female
Birth Date: 16 Aug 1833
Birthplace: Glasgow, Lanark, Scotland
Father's Name: James Jack
Mother's Name: Ann Bowman
Cecilia Jack
Event Type: Christening
Event Date: 15 Oct 1835
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original): Glasgow, Lanark, Scotland
Gender: Female
Father's Name: James Jack
Mother's Name: Ann Bowman
Janet Jack
Event Type: Christening
Event Place: Glasgow, Lanarkshire, Scotland, United Kingdom
Event Place (Original): Glasgow, Lanark, Scotland
Gender: Female
Birth Date: 21 Dec 1837
Birthplace: Glasgow, Lanark, Scotland
Father's Name: James Jack
Mother's Name: Ann Bowman