I have had opportunity to be with a number of people at the time of their deaths. Each time they were "sleeping" and not able to respond. I believe that in every case the hearing is there until the end, even though the person is unable to show any kind of response. Always I touched, talked to them and sang songs either from a hymnal (songs they loved) or songs of praise and worship that came to mind. If I knew they were believers I talked about the wonders of what they were about to experience. If I didn't know I shared God's plan of salvation for us and my own love for Jesus. I would tell them that now is the time to admit their sin and need for Jesus to wash it all away and make their hearts new. Lead them in prayer and pray with them. I always felt it very important to tell them it's okay to let go now. I would tell them " you know what else? My grandpa Nelson is in heaven with Jesus and when you get there he's gonna know that I love you and he's going to wrap his big strong arms around you and say welcome.
Unlike the True and Living God, Satan cannot be in more than one place at a a time. Demons are active in our world today. They are all about doing Satan's dirty work. One day every knee shall bow (even Satan and his demons), and every tongue confess that Jesus Christ is Lord God. They will be about that business until the time that God casts them along with Satan into the lake of fire for eternity.
When my grown daughter was pretty young she had awful nightmares where she would be crying and screaming, and I would go in and hold her or lay my hands on her and repeat the name of Jesus over and over until she calmed down and slept. She never remembered her dreams. She had given her heart to Jesus before this ever began and I can't remember how long this went on. One night she woke me with her crying out and I flew into her room and held her tight. Suddenly I had a strong feeling of being watched and I turned my head to the doorway which was backlit by the kitchen light. I saw siloetted in the doorway the form of a tall slender man leaning on the sill looking at us. I raised my hand and pointed straight at him and said "This child belongs to Jesus Christ and He is the Lord of this house. In the name of Jesus leave this place and never return!" I remember it like it was yesterday. My teeth hurt from having them clenched so tight when I spoke. I turned to my daughter and when I looked back the figure was gone. My daughter never had another screaming nightmare like that again. When her own daughters have had a bad dream she holds them and repeats the name of Jesus until the sleep peacefully again.
There is power in His name and we hold the right to call upon that power. I may not have read every post of the original poster but
if you are a believer you can do the same for this man as I have done with my friends and loved ones. Put yourself in a position where you can speak quietly within his hearing (or in his ear) and talk to him of these things. If he begins to carry on as you've said then lay a hand on him and call upon the name of Jesus Christ to order away any one/ones who may be tormenting him, and tell them never to return. They all know exactly who Jesus is. They saw Him die that day on that cross. And they celebrated with their master because they thought they'd won because they'd killed Jesus. But oh, can you imagine their surprise when after 3 days in hell Jesus flung open those gates and walked out having paid our sin debt? That's what should drive us. That's what should move us to share the love of Jesus with ones laying near death, whether they are known to be a believer or not. I wish I could have been with my grandpa Nelson when he died. He pointed individually to every family member in the room and said "I love you, and I love you....." Even to my step dad who had sexually abused me and my sisters. Jesus died for him just like he did for me. I hope he had reconciled himself to Jesus before he died and his sins were washed away. Because if he didn't then he'll spend his eternal life (and everyone has one) separated from God, which is what hell is, and worse than any pain he could have suffered here on earth.
I went on long, but I won't apologize. This is serious stuff. You may be the only/last chance for this man to hear the name of Jesus in this his on earth. I hope you will pray about it and step up and out in your faith and trust God for the right words to say. He will ALWAYS give them. I will be praying for you, this man and his family. God Bless.