Can I defend my brother?

Sure, but the judge will appoint a lawyer to defend your brother.

Article 32 of China's Criminal Procedure Law: In addition to exercising the right of defense, a criminal suspect or defendant may entrust one or two persons as defenders. The following persons may be entrusted as defenders:

(1) lawyers;

(2) A person recommended by a people's organization or the unit to which the criminal suspect or defendant belongs;

(3) Guardians, relatives and friends of criminal suspects and defendants.

A person who has been sentenced to punishment according to law or deprived of or restricted personal freedom shall not act as a defender.

Article 34 In a case where a public prosecutor appears in court for public prosecution, if the defendant fails to entrust a defender due to financial difficulties or other reasons, the people's court may appoint a lawyer who undertakes the obligation of legal aid to defend him.

If the defendant is blind, deaf, dumb or a minor and has not entrusted a defender, the people's court shall appoint a lawyer who undertakes the obligation of legal aid to defend him.

If the defendant may be sentenced to death without entrusting a defender, the people's court shall appoint a lawyer who undertakes the obligation of legal aid to defend him.

If your case is a private prosecution case, you can't have legal aid.