Section 63. The school committees of such towns shall, for the purposes of the union, be a joint committee and shall be the agent of each participating town, provided that any school committee of more than three members shall be represented therein by its chairman and two of its members chosen by it. The joint committee shall annually, after completion of annual elections in all of the member towns meet at a day and place agreed upon by the chairmen of the constituent committees, and shall organize by choosing a chairman and a secretary. It shall employ for a three year term, a superintendent of schools, determine the relative amount of service to be rendered by him in each town, fix his salary, which shall not be reduced during his term, and may provide for fringe benefits, and other conditions of employment, including but not limited to, severance pay, relocation expenses, reimbursement for expenses incurred in the performance of duties or office, liability insurance, and leave for said superintendent and shall apportion the payment thereof in accordance with section sixty-five among the several towns and certify the respective shares to the several town treasurers. He may be removed, with the consent of the department, by a two thirds vote of the full membership of the joint committee.