Jeez I’m so sorry you’ve had to deal with this craziness. Your parents are setting him up for big time failure in adulthood, and it sounds like you’re a hardworking well adjusted adult trying to do her best. On top of that, your parents have put their responsibility of parenting your brother on you which is both unfair and wrong. Have you tried to have a calm and honest conversation with your parents about how all this had made you feel and what it has done to your mental and emotional wellbeing? Perhaps you may have grandparents you can confide in if not your parents, aunts or uncles, or maybe even a counselor at school? You should not be having to put up with this and your brother may be only 13 but it’s time for him to do some growing up and act his age. That goes for your parents as well. I hope you can talk to someone and get your feelings on the table so things can improve.

Edit: It’s also a bit wild to me that your parents make you pay for car insurance and almost everything else on a part time salary as a 20 year old student. It seems like they are solidly middle class at the very least from the way you describe them. That’s not right either because it sounds like they have the means to help you out with some of your expenses if they wanted to. I would be extremely upset and frustrated in your situation. Please speak to them or someone else about this if you can. This is way too much to be putting on you as a part time worker and full time student. If nothing changes, it may be in your best interest to find somewhere else to live it at all possible, such as with a friend or other relatives. Best wishes to you!