You've been through a lot, no mistake! To help you to understand the depth of narcissism: they do not acknowledge accountability for the damage that they inflict, unless they are willing to recognize that they are a part of a horrific cycle.
You are not responsible for the actions of others, your sister, included. You have endured an enormous amount of loss, trauma, etc. The best possible course of action would be to seek the help of a psychotherapist or counselor that specifically addresses domestic violence and abuse.
Not all narcissistic relationships are between men/women or husbands/wives. Thanks for YOUR post - it gives credence to others who have suffered similar abuse from siblings!