California Codes, Code of Civil Procedure - CCP, Part 2 — Of Civil Actions, Title 3 — Of the Parties to Civil Actions, Chapter 5 — Permissive Joinder, Section 378
(a) All persons may join in one action as plaintiffs if:
(1) 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 these persons will arise in the action; or
(2) They have a claim, right, or interest adverse to the defendant in the property or controversy which is the subject of the action.
(b) It is not necessary that each plaintiff be interested as to every cause of action or as to all relief prayed for. Judgment may be given for one or more of the plaintiffs according to their respective right to relief.
Notes
Allows multiple plaintiffs to join when their claimed relief arises from the same transaction or series and presents a common factual or legal question, or when they share an adverse claim or interest in the same property or controversy. Plaintiffs need not share every claim or requested remedy, and judgment may reflect their respective rights.
Use as reference
Lexinter.net | California Code, Code of Civil Procedure - CCP § 378 | https://laws.lexinter.net/codes/california/code-of-civil-procedure/part-2/title-3/chapter-5/section-378