the bible refers to many of these "extraterrestrials" as annunaki / nephilim and the seed of the serpent.

No, it doesn't.

"Annunaki" is not a word in the Bible; it is neither Hebrew nor Greek. It comes from the Sumerian language and refers to the highest-ranking gods in their pantheon. It is also found in the languages of the Akkadians and later the Assyrians and Babylonians, who displaced the Sumerians.

"Nephilim" is in the Bible, but it does not refer to extraterrestrials. In Hebrew, it simply means "giants" and refers to humans prior to the Flood as well as some people who were of large stature that the Israelites encountered in Canaan (Numbers 13:33). Two such individuals were Goliath and King Og of Bashan (1 Samuel 17:4; Deuteronomy 3:11).

The "seed of the serpent" isn't found word-for-word in the Bible, but I presume you're referring to Genesis 3:14-15, which says:

And the Lord God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life: And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.

Who is the serpent? According to Revelation 20:2, it's Satan.

Who are the seed, or children, of Satan? According to John 8:42-44, they are wicked people, just as righteous people are called the sons and daughters of God (2 Corinthians 6:17-18).

The confusion regarding the term nephilim comes from the unbiblical Book of Enoch, which claims that the "sons of God" mentioned in Genesis 6:4 were angels that had sex with human women and that the giants were their offspring.

There are multiple problems with this interpretation. Firstly, while the term "sons of God" can be applied to angels, this only appears to be the case in three places (Job 1:6; 2:1; 38:7). Even then, it's not entirely clear whether the beings spoken of in those verses are angels or extraterrestrials from unfallen worlds. Meanwhile, all other instances of the phrase "sons of God" in the Bible refer to righteous humans.

Secondly, we know that angels do not marry (Matthew 22:30; Mark 12:25; Luke 20:35-36) but according to Genesis 6:2, the "sons of God" took the "daughters of men" as wives for themselves. If we then still assume that these "sons of God" were angels, then by marrying human women they would be going against the will of God and would've became fallen angels. However, there are no accounts of any more angels having fallen after the War in Heaven, which took place prior to the time period recorded in Genesis 6. Also, fallen angels, like wicked humans, are never referred to as "sons of God."

In actuality, the "sons of God" and the "daughters of men" are the descendants of Seth and Cain, respectively. Just like today, the children of each generation took after their parents; the descendants of Seth were righteous (Genesis 4:25-26; 5:1-32), while the descendants of Cain were wicked (Genesis 4:1-24). Over time, members of these two bloodlines mingled and the righteous compromised with the wicked, which led to nearly all of humanity becoming thoroughly evil (Genesis 6:5, 11-12). Noah, who was a descendant of Seth, was an exception to this (Genesis 6:8-9).

the bible refers to many of these "extraterrestrials" as annunaki / nephilim and the seed of the serpent.

No, it doesn't.

"Annunaki" is not a word in the Bible; it is neither Hebrew nor Greek. It comes from the Sumerian language and refers to the highest-ranking gods in their pantheon. It is also found in the languages of the Akkadians and later the Assyrians and Babylonians, who displaced the Sumerians.

"Nephilim" is in the Bible, but it does not refer to extraterrestrials. In Hebrew, it simply means "giants" and refers to humans prior to the Flood as well as some people who were of large stature that the Israelites encountered in Canaan (Numbers 13:33). Two such individuals are mentioned by name: Goliath and King Og of Bashan (1 Samuel 17:4; Deuteronomy 3:11).

The "seed of the serpent" isn't found word-for-word in the Bible, but I presume you're referring to Genesis 3:14-15, which says:

And the Lord God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life: And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.

Who is the serpent? According to Revelation 20:2, it's Satan.

Who are the seed, or children, of Satan? According to John 8:42-44, they are wicked people, just as righteous people are called the sons and daughters of God (2 Corinthians 6:17-18).

The confusion regarding the term nephilim comes from the unbiblical Book of Enoch, which claims that the "sons of God" mentioned in Genesis 6:4 were angels that had sex with human women and that the giants were their offspring.

There are multiple problems with this interpretation. Firstly, while the term "sons of God" can be applied to angels, this only appears to be the case in three places (Job 1:6; 2:1; 38:7). Even then, it's not entirely clear whether the beings spoken of in those verses are angels or extraterrestrials from unfallen worlds. Meanwhile, all other instances of the phrase "sons of God" in the Bible refer to righteous humans.

Secondly, we know that angels do not marry (Matthew 22:30; Mark 12:25; Luke 20:35-36) but according to Genesis 6:2, the "sons of God" took the "daughters of men" as wives for themselves. If we then still assume that these "sons of God" were angels, then by marrying human women they would be going against the will of God and would've became fallen angels. However, there are no accounts of any more angels having fallen after the War in Heaven, which took place prior to the time period recorded in Genesis 6. Also, fallen angels, like wicked humans, are never referred to as "sons of God."

In actuality, the "sons of God" and the "daughters of men" are the descendants of Seth and Cain, respectively. Just like today, the children of each generation took after their parents; the descendants of Seth were righteous (Genesis 4:25-26; 5:1-32), while the descendants of Cain were wicked (Genesis 4:1-24). Over time, members of these two bloodlines mingled and the righteous compromised with the wicked, which led to nearly all of humanity becoming thoroughly evil (Genesis 6:5, 11-12). Noah, who was a descendant of Seth, was an exception to this (Genesis 6:8-9).