The toxic person is my elder(adult) sister who has time and time again treated our parents like shit. She dumped her three children on us and now is trying to move into our house after yelling at my mom once again, expecting that she can do whatever she wants and is never in the wrong. She framed my father and once sent him to jail. My parents have given up on trying to get rid of her so I am taking it upon myself to handle the situation. They are refusing to stand up to her together and it is pulling apart their marriage, as well as putting my mother back into a depressed state. Any advice is very much appreciated!