Amun and Kebi were both ancient Egyptians. Amun was one of the first who established the Egyptian coven that warred against the Romanian coven. Kebi was an Egyptian slave chosen by Amun to make her his mate; he chose her because of her beauty and loyalty, which was subsequently magnified by her transformation. However, their relationship was never one of equal.
When the Volturi established the laws and conquered the Romanians, Amun knew that his coven would be their next target and quickly swayed to obey their new laws, and Kebi followed him. The rest of their coven was massacred after that.
With only Kebi and Amun left, they re-established what was left of the coven by trying to find talented members. Eventually, they came across Demetri, and later Benjamin. Kebi did not enjoy Benjamin's involvement because he was constantly receiving Amun's attention, but she kept her feelings to herself. Five years later, Tia joined their coven as Benjamin's mate. Although Amun wasn't fancy of the idea, he realized the benefits of having Tia in their coven; subsequently, Kebi became content that Benjamin's bond to Tia weakened his bond to Amun, so she could have him more to herself.
When the Cullens sought the Egyptians out for aid, Amun was immediately resistant to the idea even after the proof was presented, but Benjamin's subtle threat of disbanding their coven forced him to stay, and Kebi stayed with him.
Amun and Kebi left the confrontation before everyone else. In the movie adaptation, they remain with the Cullens throughout the entire confrontation, but leave right afterwards.