Hi Christina,
What do you know about Duncan Seaton's father? There is a very large gap between the birth of John in 1738 and Beatrice in 1752. Did he enlist in the army?
You probably know this already, but if not .......
John (1738) died late 1785 or early 1786, as he was deceased when his son John was baptised (15 Jun 1786), and the OPR records that Duncan Setton (his brother) in Balrobie was the sponsor.