Hello John,
There was clearly more than one Seaborn Westmoreland in Georgia, perhaps related, I don't know, but I do know the folks you have mentioned are in my line.
John Westmoreland (1788-1848), a younger brother of the Joseph Westmoreland who married Elizabeth Simmons, mentioned in your post, was my 3g-grandfather. I have worked these folks for years and years.
I have 5 August 1774 as your Joseph's birth, I know he passed on in Texas after 1850, but not sure when. I have the same dates as you have shown for your Elizabeth Westmoreland (born 22 December 1806), and her brother Seaborn Westmoreland (born 15 November 1802), so I know we share this line.
I would enjoy exchanging information with you.
Robert Edge "Bob" Johnston