That is what the law provides for. If the board is reduced by two seats both Bove and Graber will have no seat to run for. Then when Clarke and Meegan are up for relection there will only be one seat with a four year term and one seat with a two year term. The bigger question is if it is reduced who would be vying for the two year seat?
Town law section 87(3) provides:
Whenever a proposition shall have been adopted in a town of the
first class to reduce the number of councilmen from four to two, no town
councilmen shall be elected at the first biennial town election held at
least one hundred fifty days after the adoption of such proposition.
Party nominations for town councilmen may be made and designating
petitions filed and two town councilmen shall be elected at the biennial
town election next succeeding the biennial town election at which no
town councilmen are elected, one for a term of two years and one for a
term of four years and thereafter at each biennial town election in such
town there shall be elected one town councilman for a term of four
years, in the same manner as other elective town officers in such town.
The term of office of each such councilman shall begin on the first day
of January next succeeding the election at which he was elected.