my parents dont give me a separate room although their is an extra room I have to live with my abusive sister it has damaged me alot.How to persuade my parents?

Try telling them about your whole situation because they might be so busy to see it. Tell them how you feel, it might be hard but don't worry, you can do it because what you're going through is way harder. Sit them somewhere calm and maybe your sister shouldn't be there with you because an abusive person tends to be manipulative and might change the way she acts around you to convince them that you aren't saying the truth and becomes more abusive towards you. Maybe get an evidence of her abusive behavior and ask them to get her help.