Missouri Revised Statutes Title XXXV. Civil Procedure and Limitations § 507.030. Persons having a joint interest shall be made plaintiffs--defendants, when

1. Subject to the provisions of section 507.070, persons having a joint interest shall be made parties and be joined on the same side as plaintiffs or defendants. When a person who should join as a plaintiff refuses to do so, or his consent cannot be obtained, he may be made a defendant.

2. When a complete determination of the controversy cannot be had without the presence of other parties, the court may order them to be brought in by an amendment of the petition, or by a supplemental petition and a new summons.