Hi Margt,
When looking at the Wills, and not knowing if you had been down that path or not, I just picked up on the words Portioner, Merchant, Reading Hightae etc. My initial thinking was that the 1779 Will might relate to James Richardson who married Katie/Katherine and the 1809 one possibly a descendant of theirs.
If, in 1747 Katherine was the eldest of six children she must have been born ~1730 - 1738? Do you have a date for her marriage? A search for births (SP & IGI) in Dumfries with parents James Richardson/Katherine Richardson brings up the following, all born in Lochmaben, but no records for a James, John or Mary as you would expect if the Scottish naming pattern were followed:
Katherine 1769
Margaret 1771
William 1773
Charles 1775
Charles 1776
The book reference Monica found shows that a James Richardson, merchant in Reading made a bequest around 1726, could this be the same man (Riddan = Reading.) It sits well with your John being a 'sometime merchant in Reading':
RICHARDSON JAMES 17/11/1732 LATE MERCHANT IN RIDDAN TESTAMENT DATIVE AND INVENTORY DUMFRIES COMMISSARY COURT CC5/6/9 (2 pages)
RICHARDSON JAMES 02/11/1733 LATE MERCHANT IN RIDDAN EIK DUMFRIES COMMISSARY COURT CC5/6/10
There were indeed a great many Richardsons in Dumfries, but very few Kennedys. A John and a George, both in Halleaths died around 1739, also a William Kennedy died in 1760 in Hightae (SP Wills). He may be worth considering as one of Mary’s near relatives.
It’s all ifs and buts isn’t it!
Another one:
RICHARDSON JOHN 18/03/1758 MERCHANT IN HIGHTAE, PARISH OF LOCHMABEN EIK DUMFRIES COMMISSARY COURT CC5/6/14