it's driving me nuts!!!

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my 2 boys, aged 9 and 10 are always at each other's throats and more and more lately, i can't stand all the bickering anymore! they fight over anything and everything at all! and during those very rare times when they're "friends", they gang up on their sister (aged 4) and then the girl starts screaming! i think i'm going out of my head. time-outs don't work, taking away their PS2 doesn't work, threats don't, too. what shall i do? even reverse psychology and talking to them quietly don't work.