We understand your concern and desire to maintain peace and celebration during your nephew's birthday. It's important to remember that God is our refuge and strength, a very present help in trouble. Therefore, we will not fear, even though the earth be removed, and though the mountains be carried into the midst of the sea (Psalm 46:1-2 WEB).
Firstly, we commend you for acknowledging the spiritual warfare involved and seeking wisdom and discernment from God. As Jesus told his disciples, Behold, I send you out as sheep among wolves. Therefore be wise as serpents, and harmless as doves (Matthew 10:16 WEB).
Regarding the situation with your brother's ex-wife, it's clear that there is bitterness and division being sown. Let us remind you of the following scripture -Set your mind on the things that are above, not on the things that are on the earth (Colossians 3:2 WEB). For though we walk in the flesh, we do not wage war according to the flesh; for the weapons of our warfare are not of the flesh, but mighty before God to the throwing down of strongholds (2 Corinthians 10:3-4 WEB). We pray that God will soften her heart and that He will put a guard over her mouth, keeping watch over the door of her lips. We pray in Jesus's name that this will be a time for harmony. We pray she will not use the influence of her daughters to create a hostile situation but rather that their family can find unity on this day. We rebuke the spirit of division and bitterness, and we ask God to turn this situation around for good, just as He promised in Romans 8:28 WEB: We know that all things work together for good for those who love God, to those who are called according to his purpose.
We need to make some commentary on the topic of marriage. It appears that your brother has been divorced. This should not be. God made mankind male and female, and it is God's will that they should be fruitful and multiply, becoming one flesh. A man will leave his father and mother, and will be united with his wife, and they will be one flesh. Therefore what God has joined together, let man not separate (Matthew 19:6 WEB). The Bible specifically discusses the issue of divorce. They said, Moses allowed a certificate of divorce to be written, and to divorce her. But Jesus answered them, For your hardness of heart he wrote you this commandment. But from the beginning of the creation, God made them male and female. For this cause a man will leave his father and mother, and will join to his wife, and the two will become one flesh, so that they are no more two, but one flesh. What therefore God has joined together, let no man separate. In the house the disciples asked him again about the same matter. He said to them, Whoever divorces his wife, and marries another, commits adultery against her. If a woman herself divorces her husband, and marries another, she commits adultery (Mark 10:4 WEB).
We pray for your brother, that God will heal his heart and bring a godly spouse into his life if that is His will. We pray that he will find comfort and companionship in the Lord during this time and that he, his children, and his grandsons will be drawn closer to God through this experience. We pray that your brother keeps himself sexually pure and seeks the Lord's will for his life.
Let's pray together:
Dear Heavenly Father,
We come before You, lifting up this situation and asking for Your divine intervention. Lord, we ask that You surround this birthday celebration with Your hedge of protection, and that no weapon formed against it will prosper. We rebuke any spirit of division, manipulation, and bitterness, and we ask that You fill this day with love, joy, and unity in Jesus' name.
Father, we also lift up your brother's family to You, asking that You heal their hearts and bring restoration. We pray that You will work in the life of his ex-wife and her daughters, turning their hearts towards You and Your truth. We ask that You will guide your brother in wisdom and discernment, and that You will bring a godly spouse into his life if that is Your will.
We pray all these things in Jesus's name, Amen.
Finally, let us remind you to put on the full armor of God, that you may be able to stand against the wiles of the devil. For our wrestling is not against flesh and blood, but against the principalities, against the powers, against the world's rulers of the darkness of this age, and against the spiritual forces of wickedness in the heavenly places. Therefore, put on the whole armor of God, that you may be able to withstand in the evil day, and, having done all, to stand. Stand therefore, having the utility belt of truth buckled around your waist, and having put on the breastplate of righteousness, and having fitted your feet with the preparation of the Good News of peace; above all, taking up the shield of faith, with which you will be able to quench all the fiery darts of the evil one. And take the helmet of salvation, and the sword of the Spirit, which is the word of God (Ephesians 6:11-17 WEB).
We are encouraged that you mention JESUS in your prayer request because it is true what the scripture says in John 14:6 WEB: Jesus said to him, I am the way, the truth, and the life. No one comes to the Father, except through me. For there is none other name under heaven given among men, whereby we must be saved. (Acts 4:12 WEB)
Prayer Focus: God, Thank You for loving me. God, I ask You in Jesus’ name please bless me with everything that I stand in need of and everything You want me to have. 
