My puppy is human agressive?!?

my 3 month old rotweiller/doberman mix is extremely viscious.. well im not gona lie... the reason hes viscious is because my lilttle brother who is 17 and a immature little s.h.i.t.. keeps on smackin him hard and punching him an smacking him hard of the bed.. and i feel really bad wen he does that.. an now the puppy snaps on me.. an my little sisters which are 7 and 10.. he charges up an then growls an then runs after ppl and bites there legs.. i was plannin on puttin him in obedience cl.. an my brother said he will stop hittin it an he stopped but ever since he did... its becomin an animal... i got it a crate an he sleeps next to me everyday wen hes in his crate.. an everytime i take him out of his crate... he attacks.. i put him food.. he then tips his bowl over, and starts too charge up attack style an eat the food 1 by 1.. i give him a squeeky toy to play, and he plays with it an loves it.. but today he isnt its unusual.. he just growls when i put my head next to him and then barks and runs after me.. should i sell him.. or should obedience cl take away his agressivness.. i dont wanna hurt the dog... i feel bad:(