Mom always think shes right? what to do?

OK so my mom wants my brother to take a certain college course to fulfill his biology requirements. But my grandma wants him to take a different one. So my mom is angry because supposedly my grandma was rolling her eyes at the course my mom wants my brother to take. She told me and my dad that grandma thinks she always right and doesn't want to admit she's wrong. So she wants to let grandma know that she's wrong and my mom is right. So I told her she needs to just be queit and respectful because some fights aren't worth fighting for. Grandma doesnt need to know she's wrong. Because all that matters is she knows she's right. But she yelled at me and said "GIVE ME A BREAK JEN. Psh DONT try telling me....everyone always thinks I'm the fool". And then she glared at me really meanly. Then she left and started fighting some more. I almost cried because she hurt my feelings. Im really sensitive. I was just trying to give her advice. I don't see why she's complaining about grandma. She's the exact same. But it seems like every time my brother is around. There are fights EVERY Week. Its like usually the fights are about my brother. And him being immature or she is trying to control his decisions. If she wants him to grow up. Then she needs to let go. My dad treats my brother like an adult. And tries to help my brother be independent but my mom just shelters him and tries to do his homework and whatever. I mean seriously. Just Because he's lazy doesn't mean doing stuff for him will make him better. SHES the one who turned him into that kind of person. Most of the time I just stay out of everything. But since I'm supposedly the "little" one of the familyn no one wants me to stand up for myself or say anything or know about anything because I too young.if I do state my opinion they fight back and are surprised I even said anything. I feel like a bird in a cage.