We join with you, dear sister, in lifting up this young man and your daughter to our Lord Jesus Christ. We stand on the promise in 1 John 5:14-15, "This is the confidence which we have before him, that, if we ask anything according to his will, he listens to us. And if we know that he listens to us, whatever we ask, we know that we have the petitions which we have asked of him."
Firstly, we pray for this young man, that he would turn to Jesus in his pain and surrender his will completely to Him. We pray, "Dear Jesus, You know this young man's heart and his pain. We ask that You comfort him and draw him close. Give him the strength to surrender his will to Yours, trusting that Your plans are good, pleasing, and perfect (Romans 12:2). Make him a godly spiritual leader, equipped to lead his family in righteousness."
We also pray for your daughter, that she would yield completely to the Holy Spirit in this relationship. We pray, "Lord Jesus, fill our sister's daughter with Your Spirit of wisdom and revelation (Ephesians 1:17). Guide her steps and help her to surrender her will to Yours. Grant her a spirit of forgiveness, just as You have forgiven us (Ephesians 4:32)."
Regarding their reconciliation, we pray that if it is indeed the Lord's will, this young man would lead the way. We remind you, dear sister, that God's will is always for us to be conformed to the image of His Son (Romans 8:29). His will is not for us to be unequally yoked with unbelievers (2 Corinthians 6:14). So, we pray that their relationship would honor and glorify Jesus, pointing others to Him.
We notice that you didn't mention Jesus' name explicitly in your request, but we are glad that you asked for prayers in His name. It's important to remember that it is only through Jesus that we have access to God (John 14:6). There is no other name by which we can be saved (Acts 4:12).
Lastly, we encourage both of them with Paul's words in Philippians 4:6-7, "In nothing be anxious, but in everything, by prayer and petition with thanksgiving, let your requests be made known to God. And the peace of God, which surpasses all understanding, will guard your hearts and your thoughts in Christ Jesus."