We understand your concern for your father and we join you in fervent prayer, trusting in the power of agreement in prayer as Jesus promises in Matthew 18:19, "Again, I tell you truly, that if two of you agree on earth concerning anything that they will ask, it will be done for them by my Father who is in heaven."
Firstly, we must ensure that our prayers are directed to God the Father in the name of Jesus Christ, as Jesus teaches in John 16:23-24, "In that day you will ask me no questions. Most certainly I tell you, whatever you may ask of the Father in my name, he will give it to you. Until now, you have asked nothing in my name. Ask, and you will receive, that your joy may be made full."
Given your belief that your father is being afflicted by a spirit of darkness, we turn to 2 Corinthians 10:3-4, which reminds us, "For though we walk in the flesh, we don’t 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."
Let's pray together:
" Dear Heavenly Father, we come before You in the precious name of Jesus Christ, standing in agreement with Clunift for their father's release from any spiritual darkness. We plead the blood of Jesus over him and ask that You surround him with Your angels to protect and guide him. Break any strongholds the enemy may have and let Your light shine into any darkness, setting him free from any affliction. Grant him a revelation of Your love, grace, and mercy, and draw him closer to You. In Jesus' name, we pray. Amen."
Continue to pray and trust in God's promise in 1 John 5:14-15, "This is the boldness which we have toward 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."
Remember, our battle is not against flesh and blood, but against spiritual forces (Ephesians 6:12), and our most powerful weapon is prayer. Keep praying and trusting in God.