Hi, welcome to healthcaremagic
The situation which you all are facing has become quite common,reason is more of psychological kind. your brother might had been low in his childhood being younger child and now when he is getting mature he is just apposing what u all expect from him to show his own importance. So this matter will not be solved easily consult to some psychiatrist
for his counselling
Till that time be friendly with him, give him enough space & time to express himself,dont condemn him, forget to get irritated on him, try to appriciate his positive aspects & dees as well.
Find out his best and actual friend who can persuate him about the right way of life.Because he wont listen to u at all so dont try it.
Psychiatrist will show u the way to treat him and be hopeful