Being protective of their daughter doesn’t make her parents terrible people. On the other hand, it’s not okay for a mom to tell her daughter that she hates her. It sounds like everyone is upset and may be saying things they regret.
I know it may seem romantic to be in an “us against them” relationship but that seldom works out. Romeo and Juliet were teens whose parents disapproved and we all know how that turned out!
If you want to help settle things down, you need to find a way to forge a respectful relationship with your girlfriend’s parents. That means getting to know them as people and finding ways for them to get to know you. Her parents don’t know about the wonderful qualities that your girlfriend sees. They only see a guy who wants sex with their daughter.
It might help if you and your girlfriend talked with them about how you’ve improved each other’s lives and what you hope for in the future. Show her folks that you are a substantial person. That means doing well in school, maybe having a responsible job or doing some volunteer work, and working toward goals for a good life. They may never agree that it’s okay to have sex outside of marriage but they may be able to accept you being in her life if they see you as a responsible and mature young adult.
I wish you well.