At least 2 men, who rode with Quantrill, were related to Truman. They were James J. Chiles (Truman was his nephew) and William Young. William was a brother to Truman's mother, Martha Ellen Young Truman. Martha later sued the US Government for $20,000 and was awarded $3,800.
Source: Branded As Rebels by Joanne C. Eakin & Donald R. Hale.
Rose Mary Lankford