Excluding the Lord, elders in the Cult were second to none in terms of rank within the Demonic Cult. There was a total of twelve elders, and powerful warriors or leaders of powerful clans were chosen to be elders. There were some exceptions, especially from first to sixth elder spot. These spots were passed down within the six clans. However, that didn't mean that those elders were weak. The six clans always competed to give birth to a new Lord, so they were always more powerful than most.
Other than those six elders, the other six leaders were those who were chosen to be leaders because of their own power.
9th Elder Mun Yun was a member of the high-ranked clan called the Dragon Fist Clan. He had served in the past Demon-Justice War and achieved many feats which allowed him to become an elder. Mun Yun then supported his clan to become a powerful clan which was almost as powerful as the six clans themselves. Thus, all six heirs asked the Dragon Fist Clan first.