What do i do about my parents?

I have never seen my mom and dad never actually show that they love each other they just sit around watch tv (on separate couches) and go to sleep (same bed). My father has anger issues but doesn't notice them and when my mom tries to tell him he yells at her like she is some sorta child (actually he yells at her like that about anything). He acts like he is the high and mighty ruler of The house and doesn't stop to think about telling my mom anything like if he goes out he doesn't ask her, but when it comes to her she has to get permission a few days ahead before she goes out. He is very controlling. and when my brothers or i want to go out we have to ask him and if we even ask our mom before him we get in trouble and he doesn't even consider my moms choice in ANYTHING. oh and my grandma is veryyy rude to her and my father does nothing about it. He even let his mom plan their WHOLE wedding my mom had no say in it and she just wanted a small wedding but instead she got a huge one and hated it( my mom doesn't like attention).Today she told me as we were heading home that she sometimes wishes she weren't married, but it had nothing to do with us. I asked her how often does she feel like this and she said lately a lot more. and then she told me how my dad had completely changed and how he used to be independent and went out and did stuff and was laid back but now he is dependent on so many people and thing and he hardly leaves the house (besides work) and is always angry. she also told me how she feels like she never had her to herself ( cuz she got married as soon as she was 18 and had a child a year later, but my dad was 21) (they no have been married for 21 years, but i don't think they care anymore and they just live with each other just because) my mom hasn't done anything for herself in a long time and has never put herself first it was always her husband and us(us being her kids) .she told me she just wants to worry bout us and i think thats why she doesn't want a divorce bcuz of us ( my brother= 20 years old but goes to school and has a job, other brother who is 18 but is mentally ill, and me= 15 years old) but i wouldn't mind if she did i just don't know what to do about my brother, but at the same timme i don't want my mom always unhappy and stressed. She doesn't deserve that