How to stop biting/aggression?

the problem sounds like its with the mother. She says he never listens to her or stays in his room - this sounds like he has OPTIONS! If a punishment or penalty is being carried out, she must follow through with it whatever - the child must never get the notion that the parent's will can be over-ridden! She needs to lay down basic, straightforward rules such as no aggression, no spitting, no throwing etc. If he does so he must be warned and made to apologise. If he refuses or does it again he must be given 'time out' - a short set period of time in a place where he has no distractions: a place of contemplation of his misdemeanour! If he leaves the place he must be brought back to it until he finally accepts that he has to stay there. Maybe you could agree a set of rules with his mother and both agree the penalty, so he has the same system at home as with you. Once he realises there is no question of who's in charge, he should be more co-operative.