We are truly saddened to hear about the situation with your son and your grandchildren. We will stand with you in prayer, seeking God's intervention and comfort in this difficult time.
Firstly, we commend you for acknowledging the name of Jesus Christ in your prayer request. It is only through His name that we have access to the Father and it is only through salvation in Jesus Christ that we can be saved.
Let's pray together:
Dear Heavenly Father,
We come before You in the name of Jesus, lifting up this family that is hurting and in need of Your divine intervention. Lord, You know the depth of their pain and the heaviness in their hearts. We ask that You comfort them and give them the strength to endure this trial.
Father, we pray for their son. We ask that Your Holy Spirit would convict his heart and draw him back to You. We pray that You would soften his heart towards his parents and that reconciliation would come in Your perfect timing. We also pray for his children, that they would know the love of their grandparents and that the bonds of family would be restored.
Lord, we ask that You would guide this family, giving them wisdom and discernment in how to handle this situation. Help them to be a light for You, even in this dark time. We pray that their son would see the love of Christ in them and that it would draw him back to You.
Father, we also pray for their marriage. We ask that You would strengthen their bond and that they would support each other through this trial. Help them to be of one mind and one spirit, united in Your love.
We trust in Your timing, Lord, and we ask that You would bring reconciliation and healing to this family. We ask all these things in the powerful name of Jesus Christ, our Lord and Savior. Amen.
We encourage you to remain steadfast in prayer and to continue to trust in the Lord. Remember the words of Jesus in John 16:33 WEB: "I have told you these things, that in me you may have peace. In the world you have trouble; but cheer up! I have overcome the world."
Also, remember the promise 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." God can turn this situation around for good, for you and for your son.
Lastly, we encourage you to be patient towards your son but to also be willing to discuss your beliefs. I Peter 3:15 WEB says "But sanctify in your hearts Christ as Lord, and always be ready to give an answer to everyone who asks you a reason concerning the hope that is in you, with humility and fear". Be ready to explain the hope of Christ in you if he asks.
Continue to love your son unconditionally, as God loves us. Pray for him, and trust that God is working in his life, even if you can't see it right now. Stand strong in your faith and remember that God is faithful.
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. 
