As mentioned the Godly line is Adam, the son of God, with Abel to carry out that line. Since Cain killed Able, "And Adam knew his wife again, and she bore a son and named him Seth,“For God has appointed another seed for me instead of Abel, whom Cain killed.” Genesis 4:25 in verses 26 "And as for Seth, to him also a son was born; and he named him Enosh. Then men began to call on the name of the Lord." The word men is added, Enosh means "Dedicated; disciplined", Seth, "Put; who puts; fixed" (Hitchcock's Bible names - Bible Dictionary) Eve name Seth-fixed, what Cain destroyed, for her Seed to be carried on, was fixed in Seth. Did Seth that brought back the line to carry her Seed, name his son Enosh-dedicated, because with him the line would continue to be dedicated to the Lord, to carry her Seed.
Seth carries on the son of God line of Adam Luke 3:23, 36-38 "Now Jesus Himself began His ministry at about thirty years of age, being (as was supposed) the son of Joseph, the son of Heli,.................the son of Shem, the son of Noah, the son of Lamech, 37 the son of Methuselah, the son of Enoch, the son of Jared, the son of Mahalalel, the son of Cainan, 38 the son of Enosh, the son of Seth, the son of Adam, the son of God." No mention of Cain, why? Because Cain was not the son to carry the line to, "her Seed" as in "between your seed and her Seed." Her Seed, is Jesus, which is traced back to Adam the son of God and that line were the sons of God and Cain his line being men, which Genesis 4:16-24 give Cain's line, from Genesis 4:25 through 5:32 give the line of Adam, then.
Genesis 6:1 says "Now it came to pass, when men (line of Cain) began to multiply on the face of the earth, and daughters were born to them (the line of Cain)," verve 2 "that the sons of God (line of Adam) saw the daughters of men (line of Cain), that they were beautiful; and they took wives for themselves of all whom they chose"
Where are angels introduced in the lines of Adam and Cain in the context of the history of man before the flood? With the Seed being the main story line, From Genesis to Revelation the Bible is about Jesus, His coming, His life, His return. Noah is in the line from Adam to Jesus or from Jesus to Adam, with all that being in the overall context of the Bible and chapter 4 and 5, Cain's line and Adam's line with Adam's line to carry on the Seed (Jesus). Why would the Holy Spirit introduce fallen angels into the context of the immediate story and the overall story?
The book of Enoch chapter 10 has nothing to do with the story, because it talks about angel and their crime (sin) being charged to azazeal, there is no mention of anyone other then man be charged with the crime (sins/wickedness) that were committed and the judgement in Genesis 6:5, which were the result of Genesis 6:1-4.
Genesis 6:5-8 "Then the Lord saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually. 6 And the Lord was sorry that He had made man on the earth, and He was grieved in His heart. 7 So the Lord said, “I will destroy man whom I have created from the face of the earth, both man and beast, creeping thing and birds of the air, for I am sorry that I have made them.” 8 But Noah found grace in the eyes of the Lord."
With the context of Genesis 4:16-24 the line of Cain, men, his lines women, daughters of men. Genesis 4:25-5:32 the line of Adam the son of God, his line (of men) sons of God. With the two lines marrying in Genesis 6:1-4, the results of those unions Genesis 6:5, the Lord's reaction to the sickness of man, Genesis 6:6-7, with one man finding grace with the Lord, Noah, part of the line from Adam to Jesus, Genesis 6:8.
How did angels get into that context, if the sons of God are not the line of Adam and Cain's women are not the daughters of men? The immediate context of Genesis 4:16-5:32 and Genesis 6:5-8, it doesn't fit, nor the overall context, with "her Seed" being the coming Messiah and Adam's genealogy goes to Jesus with Noah in that line.
Angel do not fit the context, you have to read into the story, out of context, pull verse out of context and go outside of the Bible, to try and make a case that the "sons of God" as being fallen angels and to say they are not fallen, is even harder to prove. Because once they leave their first estate, they are reserved in chains of darkness to judgement, that does sound like an angel that is in good standing with God.