Thank you for sharing this burden for your brother and for standing with your mother in prayer for him. It is painful to watch someone you love be changed by hurt, especially when the wounds have come from family and from friends. That kind of hurt can settle deep and make it hard to let go, and it is right to bring him before the Lord as you have been doing.
Psalm 91 is a wonderful declaration over him, that God is his refuge and shelter and that he can dwell under the protection of the Most High. Continue to speak that truth over him and ask the Lord to be that covering for him in this season when his emotions feel overwhelming.
Part of what he is facing is the need to release what has been done to him. The Scripture teaches that forgiveness is not a matter of keeping count or of saying words while still holding on inside. A forgiveness that says I forgive you but I will not forget is not complete, it is like burying something but leaving a handle sticking up so it can be pulled up again. When God forgives us through Jesus Christ, His forgiveness is total and complete, and He calls us to forgive in the same way, from the heart and by His Spirit. That does not mean the hurt was not real, but it means we are willing to let God take the bitterness away and give us His spirit of forgiveness. On our own we cannot do it, but if we are willing, God will give the capacity. A helpful prayer is simply, Lord, give me a spirit of forgiveness, take this bitterness from my heart and help me to forgive as you have forgiven me.
Emotions are real and God understands them. It is good to have deep feelings before the Lord, but our lives cannot be built on feelings alone. Feelings rise and fall, and if we follow only what we feel we will be unstable. What steadies us is building our faith and our life upon the Word of God. As your brother learns to bring his wounds honestly to Jesus and to trust what God says about who he is and what God has done for him, the Lord can steady his heart even while the feelings are still being healed. God is also able to take what has been bitter and make it sweet again as He does His work within us.
We are praying for your brother, that the Lord will comfort him, heal the hurt that has changed him, and draw him close to Jesus, who is the greatest source of healing because He brings forgiveness of sins and new life. We pray that God will soften his heart where it has hardened from pain, take away the bitterness that keeps him bound, and give him the willingness and the power to release those who have hurt him into the Lord's hands. We pray that he will experience the peace of dwelling in God's presence and that you and your mother will be strengthened as you continue to love and intercede for him.