Disclaimer: I do not believe an iota in the Apocryphal writings and
thus do not know about the pre-flood, post-flood ideas of fall of
heavenly beings (? not sure) talked about in the question. But
regarding the fall of Lucifer and the angels who joined him in heaven,
I would like to give an answer
You were correct in asserting the angels of Satan are united in working against God's kingdom, for Jesus Himself clarified this:
“And Jesus knew their thoughts, and said unto them, Every kingdom divided against itself is brought to desolation; and every city or house divided against itself shall not stand: And if Satan cast out Satan, he is divided against himself; how shall then his kingdom stand?” (Matthew 12:25–26, KJV 1900)
But, how is this unity achieved? Why do they obey Satan?
- Might is right - this is the principle of the kingdom of Satan where Love does not exist. Before fall Lucifer stood next to God. He veiled the glory of God. Notice in the following verse concerning Lucifer it is said that he is the anointed cherub that covers - to understand this, we need to look at the ark of the covenant, where the presence of God - The Shekinah, was covered by 2 cherubs. This was the position of Lucifer in heaven.
“Thou art the anointed cherub that covereth; and I have set thee so: thou wast upon the holy mountain of God; thou hast walked up and down in the midst of the stones of fire.” (Ezekiel 28:14, KJV 1900)
It stands to reason that he was one of the most highly exalted beings, continually being right next to God - and we can follow this reasoning to assume that he was one of the most powerful creatures created by God. Talking about the might of Satan, Daniel 10 says that Gabriel could not contend with "the prince of the kingdom of Persia" - a name used for Satan - and that the Arch Angel Michael, who prevailed over Lucifer in heaven (Revelation 12:7) had to come down to fight him so that Daniel could receive an answer to his prayer.
- Having chosen the side of Satan, the other angels are to partake of the same punishment as their leader - thus they partly co-operate with him in opposing God's kingdom. They do everything in their power to discomfit and defeat God in their purposes.
“And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.” (Jude 6, KJV 1900)
As the wisest among them is Satan, they naturally follow his plan in this battle
Talking about Satan's wisdom, the Bible says:
“Son of man, take up a lamentation upon the king of Tyrus, and say unto him, Thus saith the Lord GOD; Thou sealest up the sum, full of wisdom, and perfect in beauty.” (Ezekiel 28:12, KJV 1900)