Violent and Stubborn Behaviour. Help us.

My younger brother gets violent whenever he talks to us(family members). He doesn't understand basic even things... Every time gets into useless arguments, throw many tantrums. He is well aware of family's financial conditions... Still asks for money everytime. He is not completely 18 years old yet...he wants to start dog breeding business for which he is asking for 50k. He has become very stubborn, 1.5 years back after completing 10th class, he left school as he wanted to do polytechnic (now he is having compartment in maths in both the semester exams), 6 months back he took admission in 12th standard(open schooling) for which he is not studying at all, now he wants to start his own dog breeding business. He fights with parents saying that he is very intelligent, he can think what no body can. He says that my father and mother don't use their brains. He doesn't eat properly, neither does he sleep properly. He needs some counselling but we are very confused. Help us.