What is your sister's age? If she is still a minor and your parents are still legally responsible for her, they may still have some time, yet, for reversing some of their poor parenting and correcting the problems that THEY have helped to create. If not, they have a decision to make about whether or not to let her continue living with them in their home, and/or setting down some boundaries, requirements for doing so, e.g., not getting drunk. From your description, I'd guess its awfully late to be learning new and better parenting skills. But if she's still a minor, its their duty to at least try.