Your mother isn’t ruining your mental health. Your over-involvement with your parents’ fight is. You may be correct in your observations but it is your father’s job, not yours, to intervene with your mother.
Has it ever occurred to you that your mother may be ill, not lazy? Your description of her reads like someone who may be either significantly depressed or bipolar. If so, she isn’t doing what she does to hurt you. It sounds to me like she is drowning and your dad and you won’t throw her a life-preserver. You just criticize her for drowning.
If I were to see your family, the first thing I would do would be to get your mom to a doctor to make sure all is well with her medically. If so, I would then insist that she get a psychological evaluation to determine if she needs treatment for mental illness. I hope you will pass these suggestions to your Dad.
Then get out of it! Love your mom. Show her some support. But get on with your own business (school and extracurriculars) and stop using your mom’s problems as an excuse. Study in the library if home is too distracting. Get involved in after-school activities that interest you or get a part time job that will help you develop some skills. You should be building your resume in order to get into a good college or to enter the workforce as more than a beginner.
I wish you all well.