In such petition the petitioners or complainants shall be named as plaintiffs and the irrigation district, and its directors, if any there are, and all persons having interest in or claim against the district, without naming them, shall be defendants; in the course of the proceedings of said case, and at any time before the final hearing thereof, any person interested may join in said case as a party plaintiff or as a party defendant, or any party interested may intervene in said case without order of the court.