Yes, it was very familiar. Many of Quantrill's men were related to one another, brothers, brothers-in-laws, cousins, etc. Cole Younger had one brother and 3 brothers in law who rode with Quantrill. Edward Hink and Sam Constable were cousins. According to one source, Riley Crawford's mother took him to Quantrill after her husband was killed. She wanted Riley to avenge his father's death. So like you said it was a "familiar theme." I suppose the same thing happened in Kansas and other states during the Civil War.

Rose Mary Lankford