The elders to me have a very complicated relationship. It seems if they all have a common enemy than everything is good and they all focus on that, but if there is not common enemy they are one big dysfunctional family that argues and fights with one another over their vastly varying opinions, and often flop back and forth or so it seems as with what Aten did.
Im not sure that Aten is spy, I honestly think he had a change of heart and felt that Marethyu had a point about Danu talis. That's not to say though that he didnt have another change of heart down the round and flop back to the dark elder side. But who knows maybe Aten realized that Danu Talis needed to fall for the dark elders to be able to rise again in the future.