I just came across a listing for a cholera epidemic in Lexington, KY and Benjamin Carcuff is listed as died between Jun 1 and August 1, 1833 in Section of Ward 4. It was published in the Lexington Observer and Reporter Thursday, August 22, 1833. Found in www.rootsweb.ancestry.com/~kypendle/pages/cholera.html

This would explain why only MA Carkuff is listed in the 1840 census with Madison. They were in the area at that time. I have not seen a John or Isaac listed.