How to deal with a negative family member?

Hello.So my family has countless problems and my father is the one who deals with it,but those problems have made my dad so pessimistic about everything and that has influenced me,my mom and my brother.As much as we try to stay happy i see my mom "falling down" emotionally and her health is getting worse.I love both my parents a lot but i can't stand seeing my mom like that and i've tried talking to her saying she should care about her well being.All those problems have made my dad notice even the smallest things and everyday he has something to argue about with my mom.Since i am younger i can handle that stress(as much as i'd like to have stress free life) but my mom can't handle that much.Everyone notices it and i think her best friend talked to my mom about getting a divorce but she says she is staying with my dad only because of me and my brother(and I feel like a burden) because if she leaves him we wouldn't have money to live and a roof to stay.So any opinion on what to do would help me a lot.Thank you