then tell ur mom he is acting or just fake back...next time he thretens u do the same cut ur self(but not in a way thall ull kill ur self or badly hurt your self)but find a way to bleed run to your mom with a good story and bust out some acting with crying and show her your afraid even if he dint do anything, fight fire with fire...trust me it cant fail thats what i did when i was a kid and i always got my way even if it was my fault, but i did what ever i could, i had a cousin that was like ur brother he was my same age and he always literally tried to kill me, and of course his mom dint believe me, so sometimes i got like a piece of broken glass or my dads shaving blade id cut my self here and there and made a big scene, and man his mom beat the shit out em then little by little a started messing with him till the point i can kick his ass and no one would believe him (but i was an evil manipulative child) i dont know if you can pull it off, u gotta be a able to manipulate peoples emotional reactions, till this day i do that, and usually no one tryies to mess with me, i can be an angel, but if u mess with me oooh ur gonna get it!!! "its better to be on the devil's side than in his path" i say...sorry hun but thats all the advice i can give you, u gotta be almost insane and really clever to pull stuff like that, but if not then ur just gona have to deal with it...i dont know about u but, ive been rebelious since a was a little kid..so idk but good luck though