I see no real reason to think the "sons of God" were angels of any kind. The text seems pretty self-explanatory: When men and women began to multiply on the earth, the men took wives for themselves.
But, the Hebrew says nothing about marriage.
1~~Now it came to pass,
when mankind {literally 'adam - came to be used for 'mankind'}
had begun to 'become numerous'/multiply
on the face of the ground {adamah},
and daughters/'beautiful women' had been born unto them . . .
2~~that the angels {beni ha Elohiym idiom: literally sons of 'elohiym/gods}
kept watching the daughters of mankind . . .that they were very beautiful . . .
and they took/'seized passionately' to them women {'ishshah} of all whom
they examined and selected. {here is a masculine plural suffix signifying
'it happened, but was irregular'}
Vs 2.) They took and seized, passionately, the women....
It does not say,
'married' them.
Certain prudish translators shied away from that one.