I recently learned that the middle initial for John N Cahoon who changed his name to Calhoun is Nichols. I found it in a Civil War draft document in which, for some reason, the twins were listed by their middle names as: Newell Cahoon and Nichols Cahoon, while their older brother James Alson Cahoon was listed by his full name. So, it is John Nichols Cahoon, 1834-1909. This makes perfect sense since their grandmother was Mary Ann ("Margaret") Nichols. Where their father James Cahoon is buried in Wisconsin, the cemetery is predominantly the Nichols family.
Now we know.