Suicide attempts are hard to read. I have a foster niece that regularly threatened. She never cut herself but she took pills. Of course, after having her stomach pumped once, she quit manipulating my sister that way.
Please do read the book your therapist suggested. I remember feeling much like you do about that book at one point. It took years of therapy and books, etc. before I started feeling at peace with detachment (and I still struggle with it now).
One thing I've learned recently is that social workers, childrens services and other government agencies are often much better equipped to handle addicts and other family issues than a single individual. You may want to check out some options for your family members. Of course, it helps if you are ready to let go.
Another thing I've figured out is that when I numb-out, I'm in trouble. Usually it means I am in an unsustainable situation and anything that's not sustainable will eventually drag me down.
I pray that you can set the boundaries you need to. I do understand wanting to help family, I've been dealing with many siblings (I'm one of 12 children) who have issues. And at the same time, I've found out that there are options out there if I do the reasearch - options that free me.
Also, I know a really great web site called
Coping.org, Tools for coping with life's stressors that has a lot of tools that can help with anger, detachment, etc.
Prayers that you find the answers that will free you.