What is the difference between the nedes and the atmorians I was hoping someone can shine some light on this for me?

I believe this should explain it:
http://www.uesp.net/wiki/Lore:Nede

The Nedes were on Tamriel, left to Atmora, and then came back again under Ysgramor.

Nedes = collective term used to describe the indigenous men of Tamriel, primarily concentrated in Cyrodiil and its surroundings. It is also used to speak of a specific tribe of these men.
Atmorans = men from Atmora, who started migrating [back] to Tamriel in the late Merethic era. Eventually, there is considerable genetic overlap between the Atmorans and Nedes, perhaps leading to some of the confusion in definition.