Within thirty days after such official determination, the chief executive officer of such political subdivision shall appoint three persons as civil service commissioners to hold office, one for two years, one for four years and one for six years, and until their respective successors are appointed and have qualified, which commissioners shall constitute the civil service board; and, biennially thereafter, such chief executive officer shall appoint one commissioner to serve for six years and until his successor is appointed and has qualified. Two commissioners shall constitute a quorum. All appointments to said board, both original and to fill vacancies, shall be so made that not more than two members shall, at the time of appointment, be members of the same political party, and no such commissioner shall, during his term of office, hold any other lucrative office or employment under the United States or the state or any political subdivision thereof having employees classified under the provisions of this part. Each commissioner, before entering upon the duties of his office, shall take the oath prescribed for executive officers. The chief executive officer may remove any commissioner appointed by him, for lack of moral character, incompetency, neglect of duty, malfeasance or partisan activity while in office, but he shall, at the same time, file with the clerk of the superior court for the appropriate judicial district a report, in writing, of such removal, with his reasons therefor. In case of any vacancy, the unexpired portion of the term shall be filled by appointment by such chief executive officer.