i'm in a bit of an odd situation. both my brother and i have been diagnosed with chronic illnesses which we've had for years. these illnesses cause symptoms similar to those of mood disorders such as depression, irritability, anxiety, and mood swings. whenever i feel the least bit unstable, i do my best to avoid taking it out on my family, such as taking some time alone. my brother, on the other hand, is quite the opposite. he is extremely angry nearly all the time, often taking it out on my mom and calling her a stupid bitch when she tries to help him. he recently even punched a hole in his wall. he hasn't physically hurt me since we were young kids, but i'm sometimes afraid he might. my parents don't handle this situation very well, although i can't always blame them since they are afraid of him. however, they're in denial about this fear. my brother runs our house. my mom has even allowed him to drink (he's 14) on a regular basis because she "knows he will go do it anyway if I don't let him." 

having said that, my dad harbors a lot of repressed anger towards my brother. he is very calm and sweet to my brother when he is defying him just to avoid a fight, but will quickly become tense, and passive aggressive towards the rest of us, especially me. usually, he does so in an extremely immature manner, resembling a twelve year old. he blames me when my brother is late to school, claiming i should leave school to go back home and pick my brother up just because my brother doesn't want to walk. just a few days ago, my dad sent me a string of passive aggressive text messages while i was sitting in class, telling me how selfish i am for not going back home to get my brother. for the next couple of days, my dad gave me the silent treatment. then, just before a significant event in my life, he started talking to me again as if nothing happened. i didn't know what to do, so i was polite but remained somewhat unresponsive. he tried a few more times afterwards to talk to me, and, upon realizing that i wasn't giving him the same enthusiasm, became angry. he butted into a private argument i was having with my mom, and with no knowledge of what we were even fighting about, called me a bitch repeatedly. for the first time in a long time, i lost it, screaming at him and telling him to fuck off. part of it was related to the mood swings my illness emcompasses, but i think some of it was just years of anger finally expressing itself. he repeatedly called me a crazy psycho, asked me if "this is why you're seeing your psychiatrist," and took my car keys. when i tried to grab my keys from him, he bent my fingers backwards and attempted to break them. 

this isn't the first time my dad has been physically violent with my brother or me. when we were younger, he used to take karate classes and would use the moves he learned to try to break our arms when he was angry at us. now, though, his behavior is primarily manipulative. my mom used to always say that a little fear of your parents is healthy. whenever my dad acts like this, my mom seems to take his side as he is (technically) the "adult", and my brother doesn't care. i feel like i'm going crazy, and i hate being at home so much that i try to find excuses to stay at school longer or sit in my car. is this type of behavior something i should expect from my parent? am i just being overly sensitive? any advice is appreciated.