It could be that you just have a problem accepting what the Bible teaches. Jude mentions Lucifer and his angels being put in charge of this world before their rebellion against God, and the NT also mentions Satan ruling the world through his demons. Do the math. The demons are the angels that joined Lucifer in his rebellion. This isn't complicated theology.
I think there is a good chance that Genesis is the most important book in the Bible. If one doesn't have a real good handle on Genesis, it's impossible to understand the NT. For our God is the God which tells the end from the beginning.
Look, Lucifer and his angels (who were to fall with him) were cast out of Heaven to the earth and they have been wanting and planning to War with God, literally. In Genesis 6 it tells us how some of these fallen angels desired our women and took some as wives. This was a lustful desire of them, however, it also helped serve another purpose, to increase their numbers for their war with God. But as it turned out, the children that the fallen angels had with our women were a hybrid race, 1/2 angel and 1/2 man. They all had superhuman powers compared to man, but still were not pure angel. These hybrids are called the Nephilim and are not in God's plan. They can never be saved or redeemed because they are not fully human. And Lucifer got wind of the prophecy that a Messiah would be born and he knew that the Messiah had to come from a pure bloodline. And they tried to corrupt all bloodlines and block the Messiah from coming. Ah but Genesis 6 tells us that Noah's bloodline was perfect.
God caused the flood to kill every corrupt bloodline. All of the hybrid Nephilim died, and being non-redeemable do not go to heaven or hell. They wander the earth as disembodied spirits. Those spirits are Demons. Disembodied, they can't do much but if they can possess a body then they are superhuman. This is why they're always casting demons out of people in the NT.
Remember your Greek Mythology? Apollo? Zeus? All those guys. They was writing about the Nephilim! I suggest doing an in depth study of Genesis and especially Genesis 6. It is actually pretty simple who Demons are. But they are NOT fallen angels and are not good angels. If you don't think so, then please explain Genesis 6 to me and what it does mean...