In the verse you mentioned it's not demons as can be related to possession, even though there can be a relation. The word here implies the descendent of the giants, this is, the Nephilim (נְפִילִים), derived from לִנְפֹּל or even לִפֹּל both meaning "to fall", this is, they are the sons of a relation between human women (בְּנ֣וֹת הָֽאָדָ֔ם) and fallen angels or sons of the gods (בְּנֵ֤י הָֽאֱלֹהִים֙) , in this sense, angels here refer to the sefirot characterization as we can in Enoch, even though it's not in Bible, it has numerous important contributions to comprehend these concepts.
הַנְּפִלִ֞ים הָי֣וּ בָאָ֘רֶץ֮ בַּיָּמִ֣ים הָהֵם֒ וְגַ֣ם אַֽחֲרֵי־כֵ֗ן
אֲשֶׁ֨ר יָבֹ֜אוּ בְּנֵ֤י הָֽאֱלֹהִים֙ אֶל־בְּנ֣וֹת הָֽאָדָ֔ם
וְיָלְד֖וּ לָהֶ֑ם הֵ֧מָּה הַגִּבֹּרִ֛ים אֲשֶׁ֥ר מֵעוֹלָ֖ם אַנְשֵׁ֥י
Above we see Genesis 6:4 which is as follows:
4 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. (ESV)
However, there is a difference when we say about demons and the Nephilim for the first are spirits that the second have, as we see in Mark 3:11:
And whenever the unclean spirits saw him, they fell down before him
and cried out, “You are the Son of God.” (ESV)
In the Book of Revelation 16:14 we have no doubts:
For they are demonic spirits, performing signs, who go abroad to the
kings of the whole world, to assemble them for battle on the great day
of God the Almighty. (ESV)
It's known in Enoch that they will be judged in the Final Judgement according to the Book of Revelation (Enoch 51:1):
- And in those days the Earth will return that which has been entrusted to it, and Sheol will return that which has been entrusted
to it and that which it has received. And destruction will return what
Enoch was the 7th generation of Adam that went alive to the waters above the sky, he passed through these walls and merged with G'd as it tell the story in Genesis. And the verse above can be confirmed in Ezekiel 37: 1-4, Daniel 12:2, Revelation 20:13.
In judaism these bad spirits are known as Shedim (שֵׁדִים), and they'd be in the Nephilim. Also, these spirits can assume human form according to jewish book Zohar 3:276a: "There is a great mystery here, which is why 'Esther' is derived from mystery (Heb. seter), as written, "You are my hiding place (Heb. seter)" (Psalms 32:7), since the Shechinah hid her from Ahasuerus and gave him a female demon instead while she returned to Mordechai's arm(s). And Mordechai, who knew the explicit Name and the seventy tongues, did all this with wisdom. This is why the sages of the Mishnah stated that even regardless of this, a man must speak with his wife before he mates with her, because she might have been exchanged with a female demon.
We conclude saying that demons (ungodly) are spirits that can enter a body giving it a similar aspect to other bodies. That's why in Peter we see that he talks about the Nephilim not of spirits per se, for chains (as we know) can't be attached to spirits, but to bodies, (even though this can refer to spiritual chains). What is really important here is to understand conceptually, then it gets clearer.