Here is a short teaching on Demonism by Chuck Missler. In the last few minutes of the teaching, Chuck talks about fallen angels and demons.https://www.youtube.com/watch?v=lgbiVTXRGF4
Matthew 22:30 reads "At the resurrection people will neither marry nor be given in marriage; they will be like the angels in heaven."I'm curious if the "in heaven" is the key. This scripture doesn't say they don't have genetics to pass or that they can't reproduce, I would say that is stretching that scripture a bit without other scriptural references to back it. It simply says that the angels that are in heaven aren't given over to marriage. If angels have free will then they had/have the choice to follow Lucifer's rebellion to which it would be possible that they had the ability to reproduce and marry as Genesis says. Once we are in heaven the covenant relationship of marriage is no longer necessary because it is merely a foreshadow and symbol of God's love to His people i.e the church. As spoken in Ephesians "Husbands love your wives, as Christ loved the Church." We will no longer have a need for marriage because what was foreshadowing will be fulfilled. I honestly don't know a ton about demonology or their origin but these were just some thoughts that I had as I read other's posts.