Gosh I've tried so many things but I have concluded the following is the only way that works in my situation (boyfriend + sister on crack and heroin)
1. No money
2. No arguing or name calling
3. Emotional + practical support (don't get sucked in by manipulation)
4. Tell them about AA meeting or such others (but don't beg / force them to go)
5. Do not do mundane things for them such as (driving them to their court hearings, docotrs appointments or even washing their clothes)
6. No drugs within the house
7. Ask them to visit their doctor (do not force)
At the end of the day this is about us as well as them, we can only do so much and then we have to let go and allow them to live in a way that they want to and if it is too painful for us then we need to move on or out. Another human cannot and will not stop a craving or addiction it is all about having an emotional balance that let's you lead your life in a healthy way
I wish you well in your journey to peace x