Can you help me figure out how to tell my family about my issues?

I am a junior in high school and I have been feeling pretty depressed recently; anything from a lack of friends to low self esteem troubles me. I have also, I'm sorry to say, felt pretty sadistic lately; occasionally murderous. of the few friends I have, most of them make fun of me and try to be better than me at everything, further crippling my delicate ego. I stab them with pencils sometimes when it gets really bad and I can't handle it anymore; I can see they are in visual pain when I do so but I see it as payback and there are never any teachers around to witness it so I have no motivation to stop. I don't even really feel sorry after I do it; just angry, and relieved in a way since now they know my suffering. I've only self harmed once, but I have felt somewhat suicidal. I still like my family for the most part, even though sometimes I have murderous urges towards them to. How do I tell my family about these issues I have? I can't help but feel, despite what Yahoo goers tell me, that they will be dissapointed in me or not love me. Can you help me figure out a definitive course of action for me to tell my family about my problems? Aside from the "just tell them" answer, as I said I'm afraid to just tell them...