Kisaiya Tershin has a sister, Kaelyn.
Kisaiya is the older of the two, and grew up with more of an understanding of what exactly was going on in the family. Which, by that, Kisa would mean that their father was an incessant gambler (not just games, but for get quick schemes); and their mother would spend every credit she could get her hands on upon frivolous things - sometimes at the expense of her own kids food.
Eventually they got out of there. As it happens, Kisa had a knack for Bounty Hunting and her sister had a knack for Engineering.