The commissioners of the districts consolidated into any new consolidated district shall become commissioners thereof until their respective terms of office expire or until they resign from office if the resignation is before the expiration of their terms of office. At each election of commissioners following the consolidation, only one position shall be filled, so that as the terms of office expire, the total number of commissioners in the consolidated district shall be reduced to three. However, if the agreement provides that the consolidated district eventually will be governed by a five-member board of commissioners, one commissioner shall be elected to a six-year term of office at the first district general election following the consolidation, two commissioners shall be elected to six-year terms of office at the second district general election following the consolidation, and two commissioners shall be elected to six-year terms of office at the third district general election following the consolidation.