Hi, Yes, I do believe James and Keturah were brother and sister. Keturah Married a Thomas Delay and James married a Rachel Karney. Rachel died within about less than a year of marriage (I'm guessing from child birth or something. Not sure where James went to from there, but I'm guessing he remarried.

Rachel: Birth 1797
Death Apr. 29, 1843
Married to James Nov 23, 1842 in Ripley Co., Indiana

Do you have any information that James married a Jane? He's a dead end after the marriage to Rachel. He's not buried in the same cemetery, so I'm guessing he moved on to another state?