Confrontation is not the solution to this problem. However, if the situation calls for it, one has to take a stand for their wellbeing. Your brother has the potential to become a brilliant player, but he is not getting the chance to prove himself. Your brother can calmly and coolly ask his friend for the reason for excluding him from practice, in a way that his find don't feel offended. In this case, the code of conduct of your brother should be cautious, diplomatic and calm in all the situations regarding this matter.