Archibald Douglas, 6th Earl of Angus - Abernethy's of Abernethy, Scotland

My husbands great grandmothers were Abernethy sisters. Their father was Barry Abernethy (or Abernathy) who married Almira Cobb. We can't get the connection to Abernethy, Scotland, but have papers telling about the city and also the coat of arms, and crest. We can't find the connection to when they immigrated to the United States. Any help would be appreciated.
My email is glee@wowway.com
Geraldine Borders Lee