What is the ruling on taking revenge on an unjust brother and destroying his life, when one has the ability to do so, and is forgiveness in this case a sign of weakness or compassion?

If a brother is unjust and arrogant, this is a grave offense. You mentioned that you forgive those who wrong you, and this is a good deed. It is legally permissible for the wronged to seek retribution from the one who wronged them, but forgiveness is better, and that is what we recommend. There are legal regulations for the wronged to seek retribution from the oppressor.