There shall be a Civil Service Commission consisting of three members, not more than two (2) of whom shall belong to the same political party, who shall be appointed by the Council. Of the members first appointed, one shall hold office for a term of two (2) years, one for a term of four (4) years, and the other for a term of six (6) years. Their successors shall be appointed for terms of six years. The Council shall fill all vacancies by appointment for the unexpired term.