"For if God did not spare angels when they sinned, but cast them into hell and committed them to chains of gloomy darkness to be kept until the judgment..." 2 Peter 2:4
In the Bible angels that were cast away from heaven became fallen angels while they awaited for God's Judgement.
GoD's final judgement would determine if the angel would be sent to hell for eternity or remain a fallen angel.
THE SONS OF GOD HAD MANY ABILITIES SUCH AS PHYSICAL VISIBILITY TO HUMANS, EXTRATERRESTRIAL TRAVEL, AND PHYSICAL TRANSFORMATION IN ORDER TO DECEIVE.
When fallen angels used their physical visibility it was to appear upon women in order to marry them and CONCEIVE children.
In the Bible there is records from the first batch of fallen angels doing this.
"When man began to multiply on the face of the land and daughters were born to them, the sons of God saw that the daughters of man were attractive. And they took as their wives any they chose. Then the Lord said, “My Spirit shall not abide in man forever, for he is flesh: his days shall be 120 years.” The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of man and they bore children to them. These were the mighty men who were of old, the men of renown. The Lord saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually...."Genesis 6:1-22