From Halopedia, the Halo wiki
Elders are a part of Sangheili local governments, assisting kaidons in governing their states. Elders typically confer in a hall or assembly house within a keep. An elder is given control his own client keep in their state. The wife of an elder is expected to be responsible for dealing with familial or bloodline matters, and managing the accounts of the elder's keep. In the event of the absence of an elder, the elder's wife is responsible for the keep's affairs and wields authority equal to that of the elder.
A council of elders oversee the kaidon's actions and help him make decisions or elect a new kaidon. If a council elder has second thoughts about his vote, it is considered a tradition to send assassins to kill a kaidon in order to test the true merit of the ruler's martial abilities; it is believed that a kaidon who cannot defend himself is incapable of being a true leader. However, while an elder has the right to send assassins against a new kaidon, the kaidon can put the elder to death for doing so, should he survive. If an elder who fails to have a kaidon assassinated begs for mercy in their last moments, they and their entire line will traditionally be put to death; however, if they attempt to fight back, their lineage will be granted mercy and they will only be banished from the keep. This was what Thel 'Vadamee chose to do after Koida 'Vadam had sent assassins after him.
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