score:5
First, it's important to understand what an angel is. In Doctrine and Covenants 129:1-3 it says:
1 There are two kinds of beings in heaven, namely: Angels, who are resurrected personages, having bodies of flesh and bonesβ
2 For instance, Jesus said: Handle me and see, for a spirit hath not flesh and bones, as ye see me have.
3 Secondly: the spirits of just men made perfect, they who are not resurrected, but inherit the same glory.
Both spirits and resurrected beings are considered angels.
These passages that you mention are actions of people before they died, in this case in the time of Noah. In the spirit world, there are two parts: spirit prison (usually referred to as hell) and spirit paradise (sometimes referred to as heaven). In 1 Peter3:19,20 the author is saying Jesus went and preached to those in spirit prison, and some of those people in spirit prison were those who sinned in the times of Noah.
The second passage in 2 Peter 2:4,5 refers to spirits as angels (which Mormons believe to be synonymous, but we know from the first passage what type of angels (spirits)) and how they are in hell or spirit prison awaiting judgment.
The third passage in Jude 1:6,7 mentions angels who kept not their first estate. From the Encyclopedia of Mormonism it says:
First estate refers to the unspecified period of time otherwise known as premortal life. The words "first estate" in Jude 1:6 are the King James translation of the Greek archΓ©. In other English versions the word is translated as "principality," "domain," "dominion," "appointed spheres," "responsibilities," and "original rank." In the context of Jude 1:6 each of these implies that certain intelligent beings existed in significant positions in the pre-earth life and fell from their favored status with God.
This is all part of the Plan of Salvation. Mormons believe that before we lived on earth everyone lived in the Pre-mortal life with God as spirits. He presented a plan where we could come down to earth to gain a physical body. The plan involved us (man) to have a veil placed over our mind (so we wouldn't remember the pre-earth life) and we'd have agency, or the ability to choose and act for ourselves. This would mean some would sin and fall away, thereby not retaining one's first estate, or standing with God in the pre-existence. Man would also have the choice to be obedient and be able to return to live with God again (retaining their first estate).
To be clear the wrong actions these angels performed (before they were angels, when they were men) were various sins, but it does not necessarily say what sins except that they were disobedient (1st passage), they sinned(2nd passage), and it mentions fornication and going after strange flesh (3rd passage).
emphasis added