The first consideration is the definition of the word "angel", and the next consideration is of the context of the chapter in 2 Peter 2.
The word "angel" was transliterated from the Greek "aggelos" and simply means a messenger, or envoy; one who was sent. (1) The English translations of this word should have just been "messenger".
Messengers can be either human or celestial. The Hebrew word for messenger was "malak" and that is where Malachi got his name. Malachi's name means "my messenger". (2) (3) (4) Malachi was a man, a prophet of God.
The translators made decisions based upon common beliefs of the day as to when to use "messenger" and when to use "angel". They made several assumptions which need to be discussed further.
For instance, in Matt. 11:10 which speaks of John the Immersor (Baptist), it is properly translated as "messenger".
"For this is he, of whom it is written, Behold, I send my messenger before thy face, which shall prepare thy way before thee." (KJV)
This "messenger" is the same Greek word "aggelos", Strong's Gr. 32 which is used in 2 Pet. 2:4. But, in 2 Pet. 2:4 the translators use the word "angel". They attribute celestial "angels" where they wish, and human "messengers" where they wish based upon their beliefs.
We must be more careful as some early mythology of Babylonian origin crept into 1st & 2nd century BC Jewish writings of the Babylonian Talmud with the dual theology of Persian Zoroastrianism as well as the angelology of the pseudepigrapaha and apocryphal books . (5) (6) These myths of dual gods have caused much of the confusion we have today over 2 Peter 2 and Jude.
So, whenever it appears in the texts we need to first think "messenger" and then look to see how the Holy Spirit is using it so that we can determine whether that particular messenger was a celestial one or a human one.
The context of 2 Peter chap. 2 continues from the discussion in 2 Pet. 1 of staying true to the faith and the gospel of Christ, to not depart from that faith. And, in 2 Pet. 1:1 he warns them of false prophets and false teachers. The chapter is concerned with "men" who are causing trouble in the assemblies. Peter then lists instances from history when other "men" were judged for their sins.
Every one will agree that verses 5, 6, 7, and 8 were discussing men who had been judged. But they want to make verse 4 about celestial messengers. The reason we can know that vs 4 was also about human messengers is the distinction made in verse 11.
"11 Whereas angels, which are greater in power and might, bring not railing accusation against them before the Lord." (2 Pet. 2:11, KJV)
"whereas messengers, in strength and power being greater, do not bear against them before the Lord an evil speaking judgment;" (2 Pet. 2:11, YLT)
The messengers in vs. 11 being of greater strength and power are the celestial "angels". Verse 4 is about human messengers who disobeyed God, and were cast down to the grave (tartarus). As human messengers were the prophets who were sent by God to warn of coming judgment, and as human messengers were also the Levitical priests who were to teach God's word to the people, and as human messengers included those selected by God such as Moses, then we must consider that the use of messengers in vs. 4 were most likely early prophets (Enoch was a prophet) who were leading others astray.
They are not named in 2 Peter 2:4. There is speculation about who these men were. But, as vs. 11 makes the distinction for heavenly messengers then vs. 4 cannot be speaking of heavenly messengers. As it appears in a list before those of Noah's flood it appears to be a logical time sequence that places them earlier than the flood.
Other than that we are not told. The Bible doesn't say who they were, only that they were judged and sent to the grave. Peter was warning against false teachers, and listed the consequences. The context is still about holding fast to the faith.
Additionally, the scriptures tell us that heavenly, celestial messengers know who God is, and do His will.
"Bless Jehovah, ye His messengers, Mighty in power -- doing His word, To hearken to the voice of His Word." (Psa. 103:20, YLT)
There is too much confusion about this issue, and it all stems from false teaching, pagan mythology, and a belief in dual gods which is no where taught in the scriptures.
Strong's Gr. 32, "aggelos" at Biblehub
Malachi - BehindTheName
Malak: Messenger - HebrewWordStudies
Untranslated words - here
Talmud & Middle Persian Culture - JewishVirtualLibrary
Excerpt from Angels & Angelology:
"A special category are the so-called Fallen Angels, frequently mentioned in post-biblical literature. This concept is also common to all Semitic peoples; the idea of vanquished gods or demons, who then appear as accursed and damned, is one that prevailed among all the peoples of antiquity. It is found in a special form in earlier versions of the story of the creation, in which Rahab appears in the role of the vanquished god. Although for a variety of reasons little trace has remained of the ideas upon which the Rahab legends are based, the dualistic concepts of paganism have nevertheless exerted a profound influence upon Judaism, and the concept of the existence of good and evil powers, contradicting as they did the idea of monotheism, found their way into Judaism through the story of the Fallen Angels. It must be pointed out, however, that the passage Genesis 6:1 ff., although usually quoted as the basis of all subsequent legends of Fallen Angels, has in fact little to do with this concept, as it later developed. Not only is the interpretation of "Nephilim" as Fallen Angels of a doubtful nature (see Num. 13:33), but the text contains no denouncement of the "Benei Elohim" who had married the daughters of men; on the contrary, it stresses that the children of these connections were "the heroes of days gone by, the famous men." It was only at a later stage, when the dualistic belief in the existence of evil demons had become a firm component of popular religion, that attempts were made to find biblical authority for this concept, contradictory as it was to monotheism."
Source: Jewish Virtual Library here