I love how her brother "found" people - at a new job no less - that do heroin. How does that work exactly? HR takes you around saying "everybody this Joe, the new guy in accounting, Joe, this is everybody". Then he proceeds to have a conversation with his new co-workers about what drugs they do? I'm not buying it.
If her brother really is a problem, cut him out of your life. It sounds like he is to me.
You also said you watch people shoot up every day. How can this be? What kind of position are you in where this is really a daily occurrence? Details please, but rest assured this is no environment for anyone to get clean.