There is also in the IGI an eighth (their first) child, Mary, born Eskdalemuir, Dumfries in 1847 - which at least places William back in Dumfries.
So the children were Mary 1847 in Dumfries, then in Crawford Lanark, Thomas 1849, Elizabeth 1851, James 1853, Helen 1855, Janet 1858, William 1862 and Rosina 1865.
There are LDS submissions for a Helen HOGG, 1821 Eskdalemuir, parents Thomas HOGG and Mary BELL.
And for a William KIRK, 1808 Eskdalemuir, parents Thomas KIRK and Elspet AFFLECK.
Who knows ...
Incidentally, I notice that the relevant Durrisdeer christening batch (C118232) is one of those infuriating batches where only the females have been extracted into the online IGI!
But, as Ysabeau says, William's death certificate should help as, if known, the names of his parents will be shown. And then, of course, you could search for their deaths (hoping that they survived until statutory registration) which would possibly take you back a further generation.
The 1855 birth certificate for Helen might be worth getting as, in that year, the certificates contained additional information (see the SP site) which might be helpful.
JAP