See Rule 52.06 (identical to FRCP 21) (similar to 507.050)
507.040. Permissive joinder of parties--separate trials
1. All persons may join in one action as plaintiffs if they assert any right to relief jointly, severally, or in the alternative in respect of or arising out of the same transaction, occurrence, or series of transactions or occurrences and if any question of law or fact common to all of them will arise in the action. All persons may be joined in one action as defendants if there is asserted against them jointly, severally, or in the alternative, any right to relief in respect of or arising out of the same transaction, occurrence, or series of transactions or occurrences and if any question of law or fact common to all of them will arise in the action. A plaintiff or defendant need not be interested in obtaining or defending against all the relief demanded. Judgment may be given for one or more of the plaintiffs according to their respective rights to relief, and against one or more defendants according to their respective liabilities.
2. The court may make such orders as will prevent a party from being embarrassed, delayed, or put to expense by the inclusion of a party against whom he asserts no claim and who asserts no claim against him, and may order separate trials or make other orders to prevent delay or prejudice.
Where several persons agree in writing to contribute towards the defense of a suit, and the proportion of one who fails to comply with his agreement is paid by the others pro rata, they cannot maintain a joint action, but each must sue separately for his share. Lindell v. Brant, 17 Mo. 150.
Where a certain person in making a contract signed it with his own name and that of another person, as partners, the joinder of such other person in an action on the contract was not proper on the ground that such other person was the trustee of an express trust. Megher v. Stewart, 6 Mo.App. 498, 593.
Misjoinder of parties.
507.050. 1. Misjoinder of parties is not ground for dismissal of an action. Parties may be dropped or added by order of the court on motion of any party or of its own initiative at any stage of the action and on such terms as are just. Any claim against a party may be severed and proceeded with separately.
2. A motion to drop or add parties may be made at the same time as other motions provided for in section 509.290, RSMo, and if so made, the provisions of section 509.340, RSMo, with reference to the consolidation of motions and waiver of objections shall also apply. If said motion is made at any other time, the hearing and determination thereof shall not delay the trial. Objections on account of misjoinder or nonjoinder of parties may also be raised by answer or reply.