In the case of property held by tenancy in common, if any cotenant signs a protest under this part, only the proportionate share of the frontage thereof represented by his interest therein shall be counted in determining the amount of frontage represented by the protest. If the change or modification of grade proposed by the ordinance of intention is only on one side of any street or portion thereof, only the owners of the real proeprty fronting on the side of such street or portion thereof where such change or modification of grade is proposed to be made, shall be entitled to make or file a protest under the provisions of this part.