1Pe 3:19 By which also he went and preached unto the spirits in prison;
1Pe 3:20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.
The Nephilim were fallen angels who were WHAT??? "Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing,"
The spirits in prison are WHAT??? Fallen angels by your own words. Also those fallen angels have never been and are not now "subject to be redeemed" Why???. Because there is no redemption for any fallen angel and there is no scripture that says so.
You have been wrong about this on more then one level.