Hi Daryl
You are back in the period when, as far as I've found, you need to spend a good while raking around in various archives, digging away, following leads and hunches, all in the hope of turning up
one little extra piece of information!
Have you checked the OPRs for siblings to son Robert? These sometimes contain little bits of extra info.
Have you looked to see if there are any Kirk Session records for the parish? Folk can turn up as elders, as "poor" requiring support, as tradesmen asked to do a bit of work on church property, as witnesses to someone elses's bad behavior or as the persosn responsbile for a bit of bad behaviour!
If it is a small parish, sometimes there is a better chance of the name you are looking for turning up. You can read these on the PCs at NAS on Virtual Volumes, or some originals are still kept at local archives, with digital copies being at NAS.
Best wishes
Lesley