Note the KJV translation of the Bible (as we know it today and which the WTBTS supposedly references) makes no reference to the Nephilim being fallen angels, or that the flood was intended to remove them.
As far as names, Semjaza was the leader of this group (if I recall correctly, appointed by God to be the watchers) and came out of the Sons of God (not from the Shedim or Jinn as the WTBTS claims) and there were 200 of them, during the flood they left their bodies behind (as depicted in the Bible Story book) were subsequently cast into Tartarus. So according to this account, there have been multiple rebellions in heaven, one by Sheitan (Satan) and one by Semjaza.
According to 2 Chronicles and 2 Samuel though, David and his men were the one that defeated these “descendants of Rapha in Gath”
The Nephilim being the offspring of humans and demons and leaving their bodies in the flood to then re-join Satan is a very modern re-interpretation trying to read stories about giants in the Torah as a literal source and not allegorical.
Both of those narratives and relatively accurate depictions in WTBTS Bible Story book/publications are ONLY found in apocryphal books (Book of Enoch and Jubilees).