If the injured party does not prosecute, according to the regulations on administrative penalties for public security, administrative detention and fines can be imposed at most, and no sentence should be imposed.
If the injured party sues, it must go through judicial investigation and evidence collection, defend in court, and finally confirm whether it is intentional injury or negligent injury. Intentional injury is much heavier than negligent injury.
In addition, if your brother can provide some evidence to prove that your brother took defensive actions to protect his own life when he was in danger from the outside world, he should be exempted from criminal responsibility by justifiable defense.
Now that my brother is in custody, you can't see him except your lawyer, but if you can provide judicial guarantee, you can still see him. To solve this problem, it is best to find a local lawyer who knows the procedure. If there is a relationship, you can bend the rules and meet your brother.