Hugh Isbister/Ivester

I'm looking for the parents of Hugh Isbister who sailed from Stromness, Orkney to Savannah GA aboard the "Marlborough" in 1775 as an indentured servant (as were all passengers) of Thomas A. Browne. Hugh was born in 1775 in Orkney, had a very interesting but short life in America (died 1791), fathered George, Jacob, Hugh Jr., Elisabeth, and Polly. Left will in Rutherford County NC. His parents could be George and Mary Isbister of Stenness, but that's all I know. Hope someone can help. I've written a book about Hugh and his descendents, well-documented and many photos. Have been back to the Orkneys to research. Nothing definitive yet about his parentage.