BIC:
What spirits is Peter referring to in 1 Peter 3:19 when he says that the spirit also went and preached to the spirits in prison who disobeyed long ago when GOD waited patiently in the days of Noah while the ark was being built?
In Genesis 6:2-4 it refers to the “sons of God” are these sons angels? or men?
I have always assumed the spirits “in prison” referred to those in purgatory. After Jesus died, we know he descended into the center of the earth, which is were “paradise” was. Jesus told the good thief that he would be with Him in paradise “that day”. We know that “that day”, Jesus died and descended into the center of the earth. “Paradise” was also called “Abraham’s Bosom” (Luke 16, I think).
But since the quote you provided describes the place as “a prison” it makes me think it was not paradise, but rather purgatory. So, in my opinion, the prison refers to purgatory.
Regarding Genesis 6:2-4: I think the “sons of God” were God’s elect at the time (similar to the Jews during the Old Testament, and Catholics today). Intermarrying between the “children of God” (those of the true religion) and the “children of men” (all others) had always been forbidden, both in the Old Testament, and only as an “exception” in the New (up until recently). There are some interesting stories in the Old Testament detailing the problem with “intermarrying”, between those of the true religion - “the sons of God” - and those of false religions - “the children of men”.
The following is what the footnote from the Douay Rhiems Bible says about the “sons of God”:
Footnote:“The sons of God… The descendants of Seth and Enos are here called sons of God from their religion and piety: whereas the ungodly race of Cain, who by their carnal affections lay grovelling upon the earth, are called the children of men. The unhappy consequence of the former marrying with the latter, ought to be a warning to Christians to be very circumspect in their marriages; and not to suffer themselves to be determined in their choice by their carnal passion, to the prejudice of virtue or religion.”
