This is a very painful situation. Your family is essentially asking you to choose between the people you love. This is never helpful. If you were not living at home, you would have more space to figure out for yourself whether this relationship is the one for you. I imagine it is difficult to think clearly when you are under so much pressure.
On the other hand, your parents may be on to something. They do know you well. They do love you. They may not be trying to hold you back from a relationship so much as trying to protect you from making what they see as a huge mistake.
You didn’t mention how long you and your girlfriend have been together or how much you see each other. You didn’t share why your family thinks this woman isn’t a good fit for you. I therefore don’t have a basis for giving you advice about the relationship.
What I can offer is this: Arguing back and forth with your family isn’t helpful to anyone. It would be more respectful of your relationship and of your family if you would take a step back from the arguing and do a bit more fact-finding. In a calm situation, quietly interview your family members about what they see as the problem. Don’t object or debate or rebut. Just take it in and tell them you will think carefully about what they say. Then do exactly that.
If the objections are just about not wanting to let you move on to the next stage of life, then the issue isn’t the girlfriend. It’s more about the normal transitioning that every family goes through. You are moving from being a child at home to being an independent adult. That’s a struggle for many families. If that is really what is bothering the family, deal with it directly by talking about what you can do while living at home to establish yourself as one of the adults, not still a kid.
But if your family has legitimate concerns about the relationship, you and your girlfriend can work on responding to those concerns maturely. That can help your relationship grow in new ways. It will also demonstrate to your family that you are ready to take on adult responsibilities.
If you continue to have difficulty navigating all of this, a therapist might be helpful. A therapist will have far more information than I do and may be able to offer more specific advice as well as support.
I wish you well.