It’s been a while since I read on the subject so my memory may be in error.
IIRC, fallen angels are merely fallen angels and remain as such. But the demons are souls of the Nephilim/Rephriam (et al giants) who were the offspring of the copulation between fallen angels and human women.
Please correct me if I’m in error on this!
The giants such as Goliath were the offspring of the nephilium and humans.
Thx.