This is so typical of the alcoholic and their family. When you step away to heal they all cry foul and need to keep you enmeshed to use a scapegoat. Are you drinking, drugs, as well? Many of us have found stopping drinking helps us to heal faster.
Cutting off all contact with your family is only sensible when they are harassing you like this. Please, please make your own life. You don't need these people in your life. The nieces and nephews are not enough of a reason to put yourself through this. You have the rest of your life to go to school, have a career, have a family and be happy. Believe me you can do it. It is possible.
Change your phone number and do not communicate with them. I am all for forgiving the offender, I did too. But that doesn't mean you have to take any more abuse or be responsible for anyone's happiness other than your own.
You sound young, now is the time to heal. Read through the forum, get to ACoA meetings or Alanon. Get support. We have many books in the stickies above, and many helpful posts. Read my blog, found under my name to the left.