New York Consolidated Laws, Civil Practice Law and Rules - CVP § 1002. Permissive joinder of parties

(a) Plaintiffs.  Persons who assert any right to relief jointly, severally, or in the alternative arising out of the same transaction, occurrence, or series of transactions or occurrences, may join in one action as plaintiffs if any common question of law or fact would arise.

(b) Defendants.  Persons against whom there is asserted any right to relief jointly, severally, or in the alternative, arising out of the same transaction, occurrence, or series of transactions or occurrences, may be joined in one action as defendants if any common question of law or fact would arise.

(c) Separate relief;  separate trials.  It shall not be necessary that each plaintiff be interested in obtaining, or each defendant be interested in defending against, all the relief demanded or as to every claim included in an action;  but 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 prejudice.