The Beyond — Jill Sanders

Selene never asked for the darkness that followed her all her life. It wasn't until her sixteenth birthday that something clicked, and she began to understand how to control it. She spent years jumping between foster homes, and the only steady person in her life was Scott, her foster-family brother. Finding out that she has an actual sister has been some of the only good news in her life. But when she finds out that she has a brother as well, things take a darker turn.

Scott was a lost soul. He was born into the world a bastard and would leave the world the same. But somehow he's ends up with a one-way ticket to the underworld, only he isn't dead. Yet. The only thing he regrets in his short life is not telling Selene how important she was to him.