His birth name was Amir finlay, and yes, Arian was his sister by blood.
Or one could say she was his step sister. Amir and Arian grew up togather thinking they had the same mother and father. However one fateful day their mother snapped and revealed that Amir was her love child with some random one night stand.
This made her husband, Arian's father break down and later in a fit of rage he broke both of Amir's legs. As if trying to send a message. Of course, his actions sowed a seed of hate in the heart of everyone in the family, so when they were old enough, they all moved out.
Arian and Amir couldn't stand both parents. But no matter how prideful Arian was, she was still bound by a sense of duty in her heart, so when she heard that her mother had been taken by the Dalriss family....she offered herself up to pay the dept.
Amir wasn't so dutiful and didn't care for what happened to his own mother. As such him and Arian drifted apart.