HI my name is S. and I know what you are going through with living with a addict in your family. I have one family member that is struggling right now with the whole drug seen and honestly there is no relationship that you can have with them other than love them regardless as they will need all the love and prayers they can get to stay alive.
Think of it this way, if your child had a discipline problem would you help them correct it and teach them how to act by being the model example or will you just turn and walk away.
Basically all the drug addiction is a discipline problem that they lack the will power to say no in exchange for that high feeling they get.
Now don't get me wrong because I have made it very clear to my family member that my children nor I condone what they are doing and that it is wrong, as well as set guidlines and rules that they must follow when we are present or they are present.
Also this is an excellent chance to show and explain to your child why we should say no to drugs and the effects that it could have on them as well as their family. You have no choice as to who your biological parents are, but God doesn't make no mistakes. You may not have been given to your mother for her to help you or build your self esteem or be there for you, but you may have been given to your mother to save her life, to be there for her and build her self esteem.
I know through personal experiance with my own mother as she wasn't always there for me nor did we have a smooth releationship when I was a child or growing up. But you know what she is my strongest ally now, dispite what she has done or hasn't done. She was an alcoholic when I was a child and I was put in the situation that your in right now only it's a different type of drug. Do not destroy your relationship with her by walking away completely, tough love is needed in these situations that's where your boundaries for your mother will come in. It's a long road ahead but keep your focus on the goal and the outcome, that deep down inside your mother has some issues going on and she loves you and your chidlren/sister/dad. She is just showing it in a negative way. She needs you and your sister's help as well as your dad.
Your dad can only do so much, the biggest impact on your mother is going to come from you and your sister and mostly your children. When a child comes to their parent and expresses concern or a problem, a mother responds to meet that need of a child, it's in our make-up.
Know this that when you have reached the bottom there is no other way but to go up.
I hope my words bring encouragement and hope with what ever your decision is. God Bless