As the Bible teaches us that we must distinguish between the devil, fallen angels and demons.
The word devil in Greek is called "diabolos ho" and there is only one, not used in the plural.
Demons are called "daimon" in Greek, the word is used 56 times in the New Testament, and also identified as "spirits", as Matthew 8:16, 17:18, Mark 9:25;
Luke 8:23, 10:17,20.
The difference between demons and fallen angels is that the former are disembodied spirits, without bodies, while others have a spiritual body Lk 20:35.
It is clear that demons have bodies, because they are constantly in search of human bodies to use as your own Mk 9:25, Mt 12:43-45.
In Matthew 8:31 we find that support to the bodies of pigs.
Fallen angels are instruments of Satan in his dominion over the world. The positions of authority over the nations and peoples as Dan 10:13,20, Isaiah 20:21. The "prince of the kingdom of Persia" withstood the messenger of God for 21 days and the "prince of Greece" came at him from behind. The fallen angels to fight Satan's side against Michael and his angels in heaven in the great war described in Revelation. 12:7-9. Will be launched on Earth. Since the eternal fire prepared for Satan and his angels as Mt 25:41.
There are angels chained in the darkness mentioned in the book of Jude 1:6 and the book of II Peter 2:4. They are trapped in chains and darkness, or in a place called Tartarus (Tartarus in Greek), classified by some scholars as a special place in Haddam, or, more likely, the abyss too. The reason why God does not allow them freedom is because their sin was very serious, and Jude 1:6. It may also be that they are endowed with such power that God believes in freedom are drawbacks. Certainly, it will be judged at the time of the Great White Throne.