Angels in obedience having spiritual bodies in heavens, does not marry, however it is a different story for angels that has left their heavenly abode and came on earth manifested as men and disobeyed the Lord's command to not marry. That's why Peter said they had sinned and Jude compares their sins to Sodom and Gomorrah going after 'strange flesh". The Bible is very clear on the issue.

Where does the Bible say that angels received a command to not marry? They don't marry because they aren't physical beings.
Angels (both fallen and unfallen) may assume a human appearance, but they aren't flesh and blood, so they can't procreate.

For we do not wrestle against flesh and blood, but against principalities, against powers, against the world's rulers, of the darkness of this age, against spiritual wickedness in high places (Eph 6:12).

The "sons of God" do not act that way, Elle. Those are the fallen angels, and Genesis does not say that it was the fallen ones, but rather the "sons of God" who married the daughters of Cain. Who are the "sons of God"? They are those who are obedient to God's will.

"Sons of God" can be by creation or birth by the Father like Jesus, the angels, and Adam were, or by adoption like the sons of man will become.

It is true, a true son of God will obey. And these fallen angels were in obedience before they fell. However, just because they fell does not negate the fact that they were in obedience before hand and are not pro-created beings and all of them have been created straight from the Lord's hand. Therefore their father is the Lord and these angels are His sons. That physical fact does not change whether they sin or not. Angels are referred as Sons of God in Job 1:6; 2:1; 38:7.

Adam is a son of God also for he was created by the Lord. However, all Adams offsprings were born after the fall of Adam. And the Bible is very specific that we are "Sons of men"(23 occurences in the Bible, and 193x for “son of man”).

Any man on earth today or any offsprings of Adam was or cannot be considered as a "son of God". Scripture says that we will become(future) “sons of God” by ADOPTION.(Rm 8:15; 8:23; 9:4; Gal 4:5; Eph 1:5)) That means we are still not “sons of God” nor does any sons of Seth were by Biblical definition.

The beginning of the process of becoming one starts when we are reborn by the Spirit. When we are reborn, it’s only a seed(Jesus) is in us that still needs to grow inside a body that the carnal mind is big and dominant.

There are many different stages of growth by which the types and shadows of the Law describes. The baby stage is symbolically represented by the Passover(justification). The children stage is symbolically represented by Pentecost(the offering of two leavened bread) where we receive only an earnest deposit of the spirit. But full sonship is represented by the Feast of Tabernacle by which the sons will be declared and will receive the full measure of the spirit.

This has not been fulfilled yet. So everyone is at least in the Pentecost level of growth IF they are learning to hear the voice of God for themselves. Most SDAs and other Christians are still in the Passover stage and yet that is questionable. No one will get to the Tabernacle level without going through the Pentecost stage. In that stage we are to hear and learn to differentiate the voice of the Lord apart from ours.

The Bible is very specific and refers to us as “Children of God” because children are not yet Sons until they reach full maturity and have received the fullness of the Spirit.

Also, sonship is not an individual phenomena. Many has died overcomers(through the disciplines of the Lord); however they have to wait for the resurrection to part of “the manisfestation of the sons of God"”. It is a group phenomena, for at that time, the body will be attach(Marriage) to the head(Jesus).

AV Ga 4:5 To redeem them that were under the law, that we might receive the adoption of sons

AV Ro 8:19 For the earnest expectation of the creature waiteth for the manifestation of the sons of God…. And not only [they], but ourselves also, which have the firstfruits of the Spirit, even we ourselves groan within ourselves, waiting for the adoption, [to wit], the redemption of our body.

The Bible says we are waiting for the adoption of becoming "sons of God". Rom 8:23 So reality is we are not sons yet, and only have a downpayment of the spirit, still have corruptible body, and was not given immortality yet. The glorified bodily estate that Adam had, no one has it yet and the sons of Seth did not have it either.

That's another Biblical reason why "sons of God" in Gen 6:2 cannot mean that it was talking about the Sons of Seth. This contradicts sound doctrine.

After looking closer at the verses it seems to be more clear who they were, it doesnt use the word for angels, look at Strongs:

Job 1:6 Now there was a day 3117 when the sons1121 of God 430 came 935 to present 3320 themselves before the LORD 3068, and Satan 7854 came 935 also among 8432 them.

Compare to Job's sons....

Job 1:13 And there was a day 3117 when his sons1121 and his daughters 1323 [were] eating 398 and drinking 8354 wine 3196 in their eldest 1060 brother's 251 house 1004:

Same thing in Job 2 and 38:

b 2:1 Again there was a day 3117 when the sons1121 of God 430 came 935 to present 3320 themselves before the LORD 3068, and Satan 7854 came 935 also among 8432 them to present 3320 himself before the LORD 3068.

Job 38:7 When the morning 1242 stars 3556 sang 7442 together 3162, and all the sons1121 of God 430 shouted 7321 for joy?