Hi Jill,
I've reread the info posted so far and have spotted a discrepancy. Charles Kerr (brother of John) looks to have ages 20 years between 1841-51.
It looks like maybe the 1851 is mistranscribed and he should have been 18 as his birth is recorded as 1833-
https://familysearch.org/pal:/MM9.1.1/XYM1-G4WCharles and Robert Kerr are twins
https://familysearch.org/pal:/MM9.1.1/XYM1-Z5JThe family also had a sister called Grace
https://familysearch.org/pal:/MM9.1.1/XYM1-N5J but I've not been able to find her on 1841 census, maybe she had died
Grace Cumming on the 1841 looks as if she was indeed a grandchild of Archibald and Agnes -
https://familysearch.org/pal:/MM9.1.1/XY9W-5D6. Mary Kerr was the oldest daughter of the couple.
I would reckon with the forenames and middle names used by the family in Australia, this family and the family of Paterson's who came from Ochiltree ( not far from Cumnock
) are the best candidates for your couple John and Jane Kerr's families. I know you have box maker as the occupation of Jane's father James and on the 1851 Census he's a hand loom weaver but it's very possible he had been a box maker. The area of Mauchline/Cumnock was well known for making boxes at this period, as you may already know. Just in case you don't here's a link to Mauchline Ware -
http://www.mauchlinevillage.co.uk/ware.html.
James Paterson could have been one of many employed in this occupation but perhaps moved his family to Glasgow and changed jobs to try and better himself and his family's prospects
.
I still can't find the Paterson Family on 1841 Census
apart from Barbara and Andrew who as you know from your other thread are with their grandparents in Ochiltree.
Lastly Charles Kerr born 1833, John's brother may have emigrated too. To the USA. There is a Charles K
arr resident in New Jersey, born 1833 Scotland with a wife and two children on the 1970 US Census. He's also on the 1880 as Charles Kerr
https://familysearch.org/pal:/MM9.1.1/MN8C-J14with the occupation of Carpenter and a first born son Robert (after his twin??) . Of course it could be another Charles Kerr.....
Looby