Each clan elects one for their clan name.
They even have President of Clan Vang, VP of clan said, Treasurer of clan, Representative of Clan Said of regeion, and etc... for each clan. The organization chart is similar to that of any organization out there. So once you have your President, there are some who are elected to the 18 xeem. Does not necessarily have to be the President who is on the board but it could be one of his people. With all that said too, when it comes down to it, the OG still runs the show because the 35-50 year old still consult with the 60-80 year old. Traditional clan ranking such as ELDER still applies but at times negatable but that would negate both leader authority in the future so people avoid such drama.
18xeem can be considered the Hmong Senate of all Hmong in that region.