You've made a lot of progress since our last e mail exchange. I've got copies of some of the Parish records for Okney--Marriages/Births/Christenings.
I'm not absolutely certain I am interpreting these correctly, but on page 1,118 (Batch film# C110232) Special sheet
0344, there is a marriage listing for:
James Groundwater/Grisl Wilson 12 June 1720 in Orphir, Orkney. Parents: James Groundwater/Katherine Inksater.
On page 1,123
there is a listing for a Magnus Groundwater 20 October 1726. It actually appears to be a marriage listing, but that doesn't make any chronological sense. There is a "Jean Hay" listing within this entry.
Parents are listed as James Groundwater/Grisl Wilson.
References are Batch film# C11032 and A 458003, special sheets # 2044 and 0596
I'll try to scan these two sheets and send them to you