In the mirror universe, the House of Duras was one of the Great Houses within the Klingon Empire during the 23rd and 24th centuries. Its members included Duras, his descendant Ja'rod and his children Duras, Lursa and B'Etor.
Although the House of Duras had been prominent in the Klingon Empire for several generations, they had never been in the favor of the Klingon-Cardassian Alliance. In order to undermine the Alliance, Ja'rod attempted to forge a pact with the Romulan Star Empire. However, he was assassinated by Mogh on Khitomer before he could meet with the Romulan envoy. Although he had failed to create the pact, his sacrifice drew the House of Duras to the attention of Memory Omega, who allied themselves with his son Duras. (TNG - Mirror Universe short story: "For Want of a Nail")
This arrangement ultimately proved vital to the long-term goals of Memory Omega as, when Duras ascended to the position of Regent of the Klingon Empire in 2378, he maneuvered the Klingons into accepting a peace treaty with the Terran Rebellion. (ST - Mirror Universe novel: Rise Like Lions)
In contrast to their brother, Ja'rod's daughters Lursa and B'Etor were ignorant of the existence of Memory Omega, remaining loyal to the Alliance until they were killed by Deanna Troi on Betazed in 2371. (TNG - Mirror Universe short story: "The Sacred Chalice")