> Nephilim are angels
This is a bigger issue. The idea that "sons of God" refers to angels is disputed at best, and basing an entire theological (and especially a soteriological) paradigm around such a disputed passage is either ignorant or intellectually dishonest. Cf., for example, the thorough exegetical analysis from Keil and Delitzsch which you can read here:
https://biblehub.com/commentaries/kad/genesis/6.htm