Mammon by J. B. Thomas

Random House, 2011. ISBN 978 1 74275 074 3.
Grace and Joe are brother and sister who live with their parents in Border City. Joe is having anger problems and when he does a dark cloud forms. Grace is able to communicate with him telepathically. In the city is the very rich and charismatic Mammon Jones who also happens to be a demon.
After their parents are killed Joe and Grace discover their true heritage.  Their parents were part of the sarsareh, mercenaries who hunt demons.  Joe is considered extremely important to the Order as he can summon rifts which are used to dispose of demons.
He is known as a Ferryman. Grace is a gifted telepath and can control people by implanting suggestions. Together they join the Order where Grace is strongly attracted to Ivan one of the leaders of the Order.Joe becomes increasingly alienated and falls under the spell of Mammon who is trying to win him over to open a rift that will allow a demon army to invade earth and take over.
There are plots within plots, plenty of action and a blossoming romance between Ivan and Grace.
All of this should appeal to older teenagers as the ending leads on to a sequel.
David Rayner