Angus MacMillan

Angus MacMillan was the father of Elizabeth McCormick, who was the second wife of William McCormick.

Apparently not this Angus McMillan, even though the birth and death dates and location would be plausible: https://www.findagrave.com/memorial/175095315/angus-mcmillan It can't be him because he doesn't have a child called Elizabeth or a child who married a McCormick.