Lore for Thrynn and Dae’Kesh:
Darth Kesh was a powerful Sith, who had had two sons, one to his human wife, and one to a Sith slave. His son, Dae’kesh, grew to be a warrior, and was taken by the Sith to be a trained on Korriban. The other, Thyrnn, was destined to a life as a slave until he was suddenly pulled from the slaves and also sent for traning.
The brothers met on Korriban during their respective trials. Both were overjoyed to find the brother they always sensed existed, but never met. Because of the strength of the Force between them, they acted as if they had known each other all their lives. The two agreed to work, in concert for the good of the Empire, but more importantly for the good of their family. With both their mothers, and their father dead in the war, they are the only family they have left.