(a) If the provisions of this subchapter are adopted by a district, the district shall be managed, governed, and controlled by a commission composed of five commissioners, who shall be subject to the supervision and control of the board.
(b) Two of the commissioners shall be appointed by a majority of the city council of the municipality having a population of 100,000 or more, and two of the commissioners shall be appointed by a majority of the commissioners court.
(c) The chairman of the commission shall be the fifth member and shall be elected by majority vote of the city council and commissioners court meeting in joint session called by the county judge.