Did the angels really had sex with women and produced the Nephilim?
How is it possible that spirits can have intercourse with carnal?
This no longer happens, God put a stop to it. But in the day of the created Earth, the fallen angels, the demons, could not have their glorified bodies, they were stripped of them, therefore had to possess flesh or things, they had to be IN something. A legion of spirits can be in one man. the abyss is anything that is not physical, such as the air, or even water, spirits have to possess physical matter of some kind, either dormant, or living, or even dead.
They would indeed take physical form in the days of Adam and Eve, using whatever means they could, animals, plants, solid matter, whatever. Consider:
Genesis 4:14 Behold, thou hast driven me out this day from the face of the earth; and from thy face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass,
that every one that findeth me shall slay me.
Who was he scared of? The only humans there at that time was Adam and Eve and himself, so who was he referring to, who was he scared of? It was the demons he was concerned about. So God marked Him, so the demons knew he was marked by God and would not come near him. But cains daughters were not marked, and those creatures did as they would with the daughters of cain, and giants were in those days. But as to powers of God the Nephilims may have seemed to have, it was only the powers that the demons would show through their own selves, being that the demons would possess these offspring. satan is the god of this world. he is a god, demons are also considered gods, because they are all immortal, and were all created by Jesus Christ as immortals. The Nephilims were half humans and half gods (devils), NOT half Angels of God.
^i^ Responding to OP