Thanks for your questions - I can’t imagine what you must be going through at this time, but pray that God will give you the wisdom and strength to cope.
It’s good that you want to respond to what is happening by following the teaching of the Bible. However, in seeking to understand what the Bible wants us to do in any given situation, we need to be careful that we don’t treat the Bible as simply a jumbled collection of sayings from which we just pick out those that seem on the topic. We need to read the Bible in context, and the whole Bible points toward Jesus as God’s word and instruction to us.
Thus, the passages that you referred to from the Old Testament part of the Bible help us to understand that God takes marriage seriously, and that the betrayal of the marriage relationship is a terrible wrong, and that there will be consequences for this (as with any wrongdoing).
But to know how [i]you [/i]should respond to this wrong that has been done against you we need, instead, to look to Jesus.
When we look to Jesus we see that we all fall short of the way that God wants us to live.
We see that we all need to depend on Jesus to deal with sin and wrongdoing, whether our sin or the sin of others.
When we look to Jesus we see that because of Jesus, God offers forgiveness to all who have sinned - even such sins as betrayal, deception and adultery.
Jesus also gives us a model of how to respond when we are hurt by others, and the example he sets us is to show love and forgiveness. Ask God to give you strength through Jesus to help you in doing this.
Romans 12, verses 17 to 21 say the following:
[b][i]Don’t mistreat someone who has mistreated you. But try to earn the respect of others, and do your best to live at peace with everyone. Dear friends, don’t try to get even. Let God take revenge. In the Scriptures the Lord says, “I am the one to take revenge and pay them back.” The Scriptures also say, “If your enemies are hungry, give them something to eat. And if they are thirsty, give them something to drink. This will be the same as piling burning coals on their heads.” Don’t let evil defeat you, but defeat evil with good.[/i][/b]
In the short space of this response, and not knowing the details of your situation, I can’t outline a complete course of action for your to take, so I would suggest that you find the help of a local minister or counsellor - someone who can help you through the process of talking with your wife and brother, someone to support you as you encourage them to see the wrongness of their actions and their need to repent, and assist you to offer forgiveness to them. I would also encourage you and your wife to get counselling to uncover & deal with what has led to this situation and guide you through a reconciliation process.