"1841, I only have one possible census return but unsure of it.
John Fleming, b. 1811, Lanarkshire, occupation - carter.
Elizabeth Fleming, b. 1811, Scotland.
NK, b. 1821, Scotland"In my view this doesn't fit as later you have...
"Children’s info from 1851""Nancy Fleming, b. 1833 Glasgow
Mary Fleming, b. 1835 Glasgow
John Fleming, b. 1840 Glasgow" Where are those children in 1841?
Mary, on her marriage in 1856 is aged 22 (b c1834)
The maiden name of her mother looks like Hindman (or similar) not that it helps us for now

What info. is given on Mary's death re parents?
Where does Mary state she was born 1861/71/81 etc. until last census prior to death?
What children (if any) are still at home with Elizabeth 1861?
Have you found marriages/deaths for Agnes/Nancy & John to see what details they have re parents?
Agnes, if she married would be post 1856 as she's using her maiden name as witness to Mary's marriage.
What led you to Ossman (whichever variant) in the 1st place?
Annie