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 379

(a) All persons may be joined in one action as defendants if there is asserted against them:

(1) 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) A claim, right, or interest adverse to them in the property or controversy which is the subject of the action.

(b) It is not necessary that each defendant be interested as to every cause of action or as to all relief prayed for. Judgment may be given against one or more defendants according to their respective liabilities.

(c) Where the plaintiff is in doubt as to the person from whom he or she is entitled to redress, he or she may join two or more defendants, with the intent that the question as to which, if any, of the defendants is liable, and to what extent, may be determined between the parties.