I ran the family tree of Nelson Knight Chapman, its up on Ancestry.
In short Nelson was the youngest son of William Chapman(Sr) and Annie Knight. His brother was Capt William Chapman(Jr) of Schnabels (FWIW he is buried at Bloomfield MO with a VA marker). He also had a brother John Sherman Chapman who was a boatman and river pilot working out of St. Louis. Makes me wonder if there was a boat burning connection or Absolam Grimes connection. Interesting coincidence in any case.