My brother slept with someone else's wife, and one day someone else's husband came to beat him. What should I do?

Although you grew up together, your brother is immoral in this matter. It is immoral for adulterers, wives and daughters to destroy other people's families. You can only persuade him to correct his mistake. If it really doesn't work, just resign from your unit and leave the city. This is the best solution. If things go on, no one can say what will happen.