How can I stop being fearful of my brothers?

Well I’m 14 ad have to younger brothers.. 10 and 8. They both have medical problems to od with there brain. but they are normal every day people. yet thye get all the attension. and I get into truble for everything. My brother who is 10 has a cemical inbalince. This causes him to be violent and throws tempertatrums. I have to baby-sit him a lot since are mom is finaly going ot work again. but I am scared of him. I have the fear that he will once again throw a hamor at my head and hit me. He has once but I moved away before it hit me. He grabs knifes and anything he can to make you scared of him. well let me tell you it works. He is seeing a person who is to help him. but he only complainsa about how he never gets to go on the PS2 (yet he plays on it the most). My momther and Father know everything about my brothers. and they know nothing about me. it hurts. I cry alone in my room and the tears turn into anger. I have so much anger built up inside me that it shows. but no one cares. bsides my 2 best friends. but we are moving. and soon I will not have them. what can I do? who do I tell my parents this? how do I keep my self away form the scaredness.? how do I tell my parents and grandparnets I want to move in with my grandparents because I feel 100% safe there?