I realize that I'm staying with your subject only very peripherally because your line and mine differ; however, you mentioned research on William Alexanders and Kentucky. Did your KY digging uncover a William in western KY from about 1790 through at least the early 1810s? He was born about 1760 + or - a couple of years. He originally settled in Logan County, but it encompassed most of western KY at the time.
I'm sorry that I can't help on the VA Alexanders, and I'd be thankful for any help from you.