I was interested to read your details re: McKees and Robert Edgar. If you buy gravestone inscriptions volume 22 County Down from Ulster Historical Foundations you will find picture of pillar monument to the McKee family. It says `In memoriam Hugh McKee of Poagsburn, son of John and grandson of Hugh McKee,who with Robert Edgar joined the army of King William the third in Scotland, fought at the battle of the Boyne and settled in Lisban 1690.
My ancestor Andrew McConnell married Margaret McKee in 1760s. Her father was John McKee of Lisban (now Lisburn). Her brother was the Hugh McKee on this monument.