When angels and humans reproduce

A population explosion took place on Earth before the Flood (Genesis 6:1 TLB). If the growth rate in the pre-Flood world was equal to the growth rate in 2000 (0.012), there could have been about 750 million people at the time of the Flood. However, given the extremely long lifespans before the Flood, the growth rate could have been much higher. Increasing the rate by just 0.001 would put the population at close to four billion at the Flood ("What was the pre-Flood Population like?" published by Answers in Genesis on January 6, 2016).

At this time, beings from the spirit world looked upon the beautiful Earth women and took any they desired to be their wives (Genesis 6:2 TLB). However, some people object to the idea that beings from the spirit world could consummate a relationship with a human. Their primary reason for not believing this is Jesus' words in Matthew 22:30. In the resurrection, they neither marry nor are given in marriage but are like angels of God in Heaven (LEB). There are two misunderstandings I have heard with how this is commonly taught:

1. People have taken this to mean that dead people become angels. This isn't "It's A Wonderful Life," and that's not true. Jesus said they would be LIKE angels of God. He never said we would be angels. We will only be like angels regarding marriage.
2. Some people have said that just because angels don't marry, they can't marry or reproduce. But again, that's reading into the words of the text. Just because they don't marry doesn't mean they are incapable, especially if they take on human form.

To summarize, this passage seems to teach that demons (fallen angels) took on human form. We know from many other places in the Bible that angels can take on the bodies of humans. That's why the Bible tells us not to neglect to show hospitality, for by doing this, some have welcomed angels as guests without knowing it (Hebrews 13:2 CSB). That's why in those days, and even afterward, when the evil beings from the spirit world were sexually involved with human women, their children became giants, of whom so many legends are told (Genesis 6:4 TLB). It would make sense that such an unnatural union would be produce offspring with abnormal characteristics.