The decree of the court determining the validity, nature or extent of any such encumbrance shall operate directly on the land as a proceeding in rem, and shall be effectual to bar all the defendants from any claim thereunder contrary to such determination, and such decree so barring said defendants shall have the same force and effect as a release of such claims executed by the defendants in due form of law. The court may, in its discretion, appoint agents or guardians ad litem to represent minors or other defendants.