Alexander Abernethy, 6th Lord Saltoun of Abernethy 3rd son John was the ancestor of the Abernethys of Barrie and Mayen. I had a hard time finding any credible information about this cadet line & the naming doesn't seem correct.
What caught my eye is two of his supposed descendants, Robert Abernathy (note spelling) who was a soldier, captured the English and transported to Virginia in 1652 and his supposed brother William Abernathy. The details for William are on a separate profile, William Abernathy who appears to be his son & the assumption is William emigrated to Wallingford, New Haven. Because of the name, they are assumed to be brothers but neither one has any actual evidence of their origins. This thread is a summary of some guesses about their family.
Finally, Robert is currently a gateway ancestor and a descendant of Edward III but he's not one of the documented ones. I was going to disconnect him but I thought I'd ask first to see if anyone had any insight, thanks!