You would need to bring a legal action in family court in which you presented medical evidence (e.g. testimony from treating or examining psychiatrists or neurologists) that your brother is mentally incompetent and cannot care for himself or make his own decisions. If you can do that, the court can then declare him legally incompetent and appoint a legal guardian, which will likely be you (though the court feels that for some reason you are not qualified to be guardian, or that it would not be in your brother's best interests for you to be guardian, it could appoint someone else). An attorney who handles cases involving the disabled or the elderly (who sometimes need guardians appointed for them) can help you with this, and you are *strongly* encouraged to retain a lawyer and not try to do this yourself--these are difficult cases, not at all like suing someone in small claims court.