One one hand if you do nothing she could die in the process. Morphine is hard on the heart. You would then have to live with the guilt for the rest of your life. I believe you love her, but I don't think ruining your life trying to help someone that refuses help is necessary.
I know it must be hell looking at her destroying herself. But you have a life to live also and deserve to be happy. Just don't loose your self, nor your brother over this. 3 life's ruined does not appear logical.
My Prayers are with you.