Bloodchoice

Temptation takes its toll, and she may lose her brother but he may lose his soul, in the third Vampire Twins thriller from the author of Bloodlust.
 
With no control over his newfound appetite, Paul seems destined to bring disaster down on his family. Trying to pass as human is tearing him apart, and he goes off to live with his father for a while, leaving Ari to pick up the pieces of his murdero...