I am fairly confident that the Robt. Alexander was Col. Robert Alexander Sr. of that part of Brunswick Co., va that was later in Lunenburg, then Mecklenburg Co's., VA.
He was the only (known) child of John & Martha [LNU] Alexander of the same spot in Brunswick Co., VA. Technically the land in the Alexander place was about 1/2 in VA & 1/2 over the line in Bute (renamed Warren) Co., NC, and just East of Hawtree Creek.
The Hicks place was on the North side of the Roanoke R. , just across the from the Alexander place; Rob't. Alexander's son, William, left the area in Nov. 1802 and settled in Hancock/Putnam Co., GA. I understand, from land records, that the Harrison's were in the same area.
I don't believe Rob't. had any siblings, but would love to find out otherwise!
Please email me direct; it'd be fun to converse on these folks.