Regarding Nephilim VS. Anakim you can just search wikipedia for
Nephilim
I could share what I learned about them in school, but frankly, its not very interesting and doesn't contribute much to how Anakim/Nephilim could be put into a mod.
However, I can express my opinion that I'd rather not see Nephilim or Anakim in Sar Elad, I don't really think they fit well, especially since as an Early Era nation, they shouldn't really have very strong units but rather focus more on commanders. An furthermore, just by reading the entry on wikipedia we can see that both anakim and nephilim would not be welcome in Sar Elad (I have further reasons, but again they are really boring)
EDIT: Link fixed, thanks Endoperez.
It was just that I forgot to add
HTTP://, so it automatically adds the shrapnel thingey at the begining.