Hi Camart, the only Paterson death I can find in the Old Parish Registers with the date "26 Sept 1842" was a child James Paterson, 3 months old, son of Thomas Paterson, but in Kilsyth, Stirling.
Can you give the sources for the death your John Paterson, Gardener at Galashiels House, and for Isabella Paterson MS Hislop.
Thank you