After all the defendants have been served with process or notified as provided in section 6656, and after the appointment of an agent, guardian ad litem or next friend, if such appointment has been made, the court may proceed as though all the defendants had been actually served with process. Such action shall be a proceeding in rem against the land, and a decree establishing or declaring the validity, nature or extent of the plaintiff's title may be entered, and shall operate directly on the land and shall have the force of a release made by or on behalf of all defendants of all claims inconsistent with the title established or declared thereby. This section and sections 6655 and 6656 shall not prevent the court from exercising jurisdiction in personam against the defendants who have been actually served with process and who are personally amenable to its decrees.