I agree with your conclusion on John R. Willis. Levi was the son of Sharod (Sherwood) Willis & Mary Ann Hunter. After Sharod died Mary Ann married Robert Boatman. Levi was a minor was went with Robert & Mary Ann to Sullivan Co.
Do you know if Martha Willis listed in the Sullivan Co., 1850 census? I would be interested in who she is living with then or if any children are listed.