My mom is a pyscho?!!!?

My mom is literally a pyscho. Don't believe me? Look at all my past answers, asking what I should do about the deranged person I'm supposed to call 'mom'. She hits me, my sister and my dad and is just an ugly person altogether. She screams at me, making fun of me because I don't have as many friends as my sister but whenever my sister goes out she has another one of her 'breakdowns' where she screeches, throws stuff, smashes our things and acts like literally, a mental patient. This has caused my to keep having anxiety attacks and I cant live like this anymore. I'm not sure if this is why, but every attack on me and my sister is triggered by watching the Freddie Mercury parts of Live Aid, which she never even went to! These 'breakdowns' have been occuring ever since April 2012, and I'm a 13 year old guy and I hate to say this, I'm feeling very suicidal lately and I just want to die so all the pain will go away. She actually said she hopes my sister is found DEAD in a ditch to teach my dad a lesson, even though he works ever day of the week and she only works one. Her bizarre behaviour only happens once a week, mainly on Fridays, but on the next day she completely forgets her actions of the night before. She hates the fact me and my sister, who is 16 in September, are growing up. My dad is turning 50 this year and my grandma (his mom) died in February and he is under so much stress and he doesn't deserve anything he gets because he is such a good dad, and man. I am torn because I have two options, and I if I take one of them, EVERYONE in my family will hate me, plus no one will believe me. 1. I tell her dad what she is really like, but I rang him when it first happened last April and all I got was shouting from him saying that his daughter would never do that, even though I had marks. My dad will hate me aswell because he still loves her (i dont know why!) and says there is no point in telling them because he couldn't do anything anyway, but she is too paranoid to believe what she's really like. 2. I let her get away with it for at least the 50-60th time and it can just happen next Friday; yay. I don't have anyone to talk to about it, my school don't have a counsellor and I can't tell my friends because it will get around school and if it does, she more than likely will actually kill me.