I think you could very well be right. I think this William is Rev Robert Hogg’s brother born in 1708.
The fasti says Alexander the son of Robert Hogg was born 11th May 1746 and dies 14th of June 1774.
Crucially, there is a William Hogg who dies in Kersmains 18/12/1791 (Old Parish Registers Deaths 803/ 10 295 Roxburgh)
The entry reads:
William Hogg, father to Alexander Hogg late tenant in Kersmains.I believe this is indeed the William Hogg who married Bettie Dickson.
Alexander Hogg and Bettie Dickson have two recorded children:
Bettie Hogg - born 21 April 1743
Alexander Hogg - born 27 January 1745The monumental inscription gives a date of death as 30.8.1823 and says in the 78th year of his age.
If this Andrew is the son of William and Bettie, then he would be 78 years and 7 months at the time of death. It’s not far out at all.
The following children are born at Kersmains with only the father Alexander recorded:
Robert - Kersmains 22/06/1771
William - Kersmains 20/02/1773
Mary - Kersmains 31/03/1775
Betty - Kersmains 22/12/1776
Alexander - Kersmains 04/11/1778
Alexander - Kersmains 21/10/1780
John - Kersmains 26/02/1783
Andrew - Kersmains 05/01/1785
Archibald - Kersmains 13/10/1788
Isabel - Kersmains 15/11/1795
Christian - Kersmains 23/08/1802
The naming of the first child as Robert niggles me. This seems to fit better for Alexander the son Robert and Mary however, the naming pattern has variations in this line. Rev. Robert Hogg’s parents Alexander Hogg and Bessie Mein name their first son for the father’s father and first daughter for the father’s mother. Rev. Robert’s grandparents Johne Hogg and Vair Ker name their first son for the mother’s father and first daughter for the mother’s mother. I think this was done out of respect for the status of the mother’s father - Wair Ker daughter of Thomas Ker Knight of Redden. I’m not really sure who Bettie Dickson’s parents were.
There is a marriage of an Alexander Hogg to an Isabel Young in 1772 Ednam - 788/ 10 250 but that would mean either Robert is illegitimate, it’s not the right Alexander (could he be the son of Rev. Robert's Alexander?) or the marriage entry is not the right one. I know Alexander is recorded as the 'fourth son' on the Kelso Chronicle entry in 1851.
We can also track Alexander from Kersmains to Homebank on the tax rolls.
1788 Alexander Hogg and Andrew Hogg Carsmains
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/horse-tax-rolls-1785-1798/horse-tax-volume-10/1221789 Alexander Hogg and Andrew Hogg Carsmains
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/horse-tax-rolls-1785-1798/horse-tax-volume-13/1321790 horse tax Alexander Homebank
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/horse-tax-rolls-1785-1798/horse-tax-volume-17/451791 horse tax Alexander Homebank
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/horse-tax-rolls-1785-1798/horse-tax-volume-20/541792 horse tax Alexander Homebank
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/horse-tax-rolls-1785-1798/horse-tax-volume-23/541794 horse tax Alexander Homebank
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/horse-tax-rolls-1785-1798/horse-tax-volume-26/571797 horse tax Alexander Homebank
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/horse-tax-rolls-1785-1798/horse-tax-volume-29/431797 watch tax Alexander Homebank
https://scotlandsplaces.gov.uk/digital-volumes/historical-tax-rolls/clock-and-watch-tax-rolls-1797-1798/clock-and-watch-tax-volume-1/39So this Alexander goes from Kersmains to Homebank around 1790. He is still having children at Kersmains though - Isabel and Christian.
Isabel (Isabella) died 1863 Greenlaw - and the parents are recorded as Alexander Hogg and Isabella Young.
Another interesting Kersmains connection is John Hogg who died in 1858 - the death certificate interestingly say the father Alexander -
Kersmains. I did wonder why it says Kersmains and not Homebank here. I thought maybe there were two Alexanders and this was a way to differentiate but the mother is also recorded as Isabel Young.
The date of death of on the MI, the children’s names and the proximity of Alexander’s headstone to his father are what causes me to question it. I don’t see any mortcloth accounts in 1774 (Roxburgh kirk session, Minutes (1722-1746, 1753-1760), Accounts (1722-1780), CH2/314/2 p477) but perhaps the family had their own. There also doesn’t appear to be a surviving headstone for Andrew in 1774.
But really I’m not sure if that is enough to say the Fasti is wrong when there is evidence to suggest William is the father of Alexander and because of the proximity to the family plot in Roxburgh we can probably deduce that William is indeed the brother of Robert.