Who were more likely cousins and we'll probably never know the answer.
I found a suggestion in a MyHeritage tree
https://books.google.com/books?id=reQZDgAAQBAJ&lpg=PA69&ots... page 145 of The Outlaws of Cave-in-Rock By Otto A. Rothert
Says that TS Smith in 1855, who interviewed eyewitnesses, asserted that Micajah was born William, son of John Harp, and his cousin Wiley was Joshua, son of John's brother Wiliiam.