Joe, The Mackenzie's Dunskey Castle & Edgar / Edzear family, does appear to have been confused with the Adair's Dunskey Castle further south near Portpatrick.
The earlier castle up north (I believe) is noted in "The Buik of the Cronicles of Scotland" (search on Google books). "How Eugenius, the King of the Scottis passit in Gallowa with ane armie aganis the Saxonis and Pechtis.
And king of Pechtis with mekle bost and schoir, By the se coist with all thair power lay, Segeand ane castell callit wes Dunskey."
Dunskey has been spelt several ways in old books, but seems to be Dun = castle; (is)KY = quay; castle by the sea (your nice photo).