Glad it was useful.
What follows is a bit of speculation.
I see that there are several baptisms of children of John Coupland in Kirkmahoe
John, baptised 16 September 1783
William Grey, 1 January 1786
James, 22 April 1791
Francis, 3 April 1793
Mary, 22 October 1797
Jean, 23 February 1800, mother's name Helen Sloan
Thomas, 25 December 1802, mother's name Nelly Sloan
I also note with interest a marriage of John Copland to Helen Sloane in Lochrutton on 18 November 1781.
And there are deaths of James Copland, aged 77, mother's surname Sloan, in Tinwald in 1868 and Francis Coupland, aged 66, mother's surname Slowan, in Mouswald in 1859.
It therefore occurs to me to wonder whether all of these children are siblings?
And is Jane Copland, who died in Morton in 1869 aged 68, perhaps one of them? I can't see obvious candidates for John, Thomas or Mary, but there are some possibles if their ages were not recorded accurately.
If you are interested in following this up, you could take a look at those death certificates and see if they are indeed children of John Co(u)pland and Helen/Nelly Sloan. If they are, I think they would point to William Grey Co(u)pland's mother being Helen Sloan.
And if so, it might be worth looking at the baptisms to see whether the names of any witnesses provide any useful clues to the parentage of John Co(u)pland and Helen Sloan.