I haven't yet read all of the posts on here yet, so I'm not sure if someone has already said this, but if you sense demonic activity then praying in the Holy Ghost (in tongues) is literally a spiritual weapon against spiritual wickidness.
I have experienced this in the past with my own family member. She is fine now and is back in right standing with Christ. (My cousin), but at one point she had been backslidden. She was sleeping around, going to clubs, and to be honest I don't know what else she had been up to. Only God knows.
A few years ago, her and my mother were at my house. My mum wanted my cousin to come over as well, but in my spirit I knew that she wasn't supposed to come. I couldn't quite put my finger on it, but my mum so desperately wanted her to come to my home as well, because we hadn't seen her for a while. My cousin ended up coming to mine and they both stayed round. It was a very hard few days, because I was literally fighting demons in the spiritual realm, almost every second. These few days was the most tangible experience I had ever had with the demonic presence. I felt them come into my home with her. It was high spiritual warfare. It didn't effect her character, so it's not like she was attacking me or my mother or anything. She's a nice girl, it's just that she was battling demons at the time, literally.
When I would go to sleep in my bed I would feel them moving on top of me. It was such a horrible feeling. Every time I would try to fall asleep I would feel them on my bed. My mother did too. My mum said she could feel them pressing the bed down, to the point she could feel them pressing the springs in the bed. This was new to me, I had never experienced anything like it before. (This kind of warfare).
The power of God was with me at the same time. I felt it. I started to pray in the Holy Ghost, and in the spirit realm I saw the demons shrinking, getting smaller. In the spirit realm they didn't look like monsters or anything graphic, they just looked like big outlined shadow figures.
I don't mean to scare anyone by saying this, but one of the nights while my cousin was still at my home, my mum physically saw a very small demonic figure, like a little goblin running through the passage way. She said it had on it's head what looked like a turban, something wrapped on it's head. Me and my mum now believe that signifies bondage, and burdens, which of course my cousin had been carrying at the time. This is a true story guys. Believe it if you want. I believe that as I prayed, the demon was shrunk to that small thing my mother saw. My mother defeated it with the blood of Jesus, so the Lord allowed her to do the finishing touches if you will, and that thing left. Thank God I wasn't the one to physically see that thing. It would have given me the creeps. I can handle spiritual warfare, but to see something physically like that would have been too creepy for me, haha. You know the saying, God doesn't give you more than you can handle lol
Well, my point in sharing this with you is to show you the important of praying in tongues, or in the Spirit, if you will. You have to attack it spiritually, and when you pray in tongues that's what you do. Yes, you can plead the blood of Jesus over the atmosphere, but the depending on the rank of demon you are fighting, you need stronger weapons at times, which was proven in the situation I experienced.
Obedience is also important as well. God told me that she wasn't supposed to come over, but my mum insisted. You see, obedience is better than sacrifice. Sometimes God will tell us things we don't always understand, but we hearken unto Him anyway, Amen... In certain situations, God will tell you to do or pray different things, because He knows how whatever you are facing needs to be dealt with. Just like when Jesus healed the blind man by spitting in the mud then rubbing it on the mans face. God will give us the direction, even if we might not logically understand it, but that's what being led by the spirit is about.
"Owe no man anything, but to love one another: for he that loveth
another hath fulfilled the law." ~ Romans 13:8