Blood Red Road by Moira Young

Saba lives with her father (her mother is dead), brother Lugh, and younger sister Emmi in a wasteland where laws do not exist. Half a year after Saba and Lugh turned eighteen, four cloaked horsemen show up, kill the father, and kidnap Lugh. The novel revolves around Saba’s quest to find and rescue her brother, with whom she has a close relationship.
Saba does not like her younger sister Emmi as she blames Emmi for their mother’s death (who died giving birth to Emmi) and tries to leave her with a family friend named Mercy, but Emmi follows Saba. The two are captured by a couple who force Saba to fight in the Colosseum for a man known as the Cage Master. The couple, Mr. and Mrs. Pinch, keep Saba fighting by abusing and threatening the life of Emmi. Saba and her sister eventually escape from Hopetown, the place where the Colosseum is located, with a fellow fighter named Jack and a group of female warriors known as the Free Hawks.
As the story progresses, Saba learns that Mr. and Mrs. Pinch are actually the parents of a king who uses an addictive drug to control people. This same king is the one who sent the four cloaked horsemen, known as the Tonton, to kidnap Lugh. Not only are more plans made to rescue Lugh, but more conflict ensues and a romance develops between Saba and Jack.