If the commissioners shall be unable to agree with the persons holding or entitled to encumbrances, rights, ways, easements or servitudes in, upon or over said land or any part thereof, for the purchase, conveyance or extinguishment thereof, or cannot satisfactorily ascertain such owners or persons, or if such owners or persons cannot execute valid conveyances for the same, the commissioners shall examine into and adjudge the true value of said rights, ways, easements or servitudes.
N.J.S. § 52:30-6