Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.

Do you have a recent and comprehensive diagnosis?? I do know there is an entire science dedicated to improving human health of all kinds. It would be the science of Medicine. If there is an answer to the problem(s), it would most likely come from there.
It begins with an evaluation, then a diagnosis, and then a treatment program. Without all of that, you are doing battle with a ghost.
I just noticed your age and to be that young, I doubt the problem is as serious as it could be if you were much older. I think your parents need to help you get at least an evaluation.
I agree you should get mental health check, but more so that you can recognize emotional abuse, and separate it from your own thoughts about yourself.
You need to protect yourself and not believe everything these people called "your family " tell you.
If you are depressed, maybe there is a councillor at school who can point you in the right direction and help you find someone to talk to. If They are the kind of family I am familiar with, they will do everything possible to help you, if there is an audience.
Now you need to be thinking about what kind of work you may be good at. Marraige should be a choice and option, imho, not a fear based arrangement. Work on yourself to be the best you, you can be.
And ps. Lots of horrible people marry. It doesn't make them good people.
And you don't sound in the least bit horrible anyway.