Plaintiff is the person that files a case while defendant is a person against whom a case is filed. There can be multiple plaintiffs and multiple defendants in a case.
A suit against multiple defendants is a civil case in which there are number of persons against whom relief is sought. In such like circumstances the plaintiff has to serve summons to all the defendants separately.
Even if different defendants in a case have same address, the plaintiff has to serve them summons separately. Each defendant has to right to defend himself separately in the case. Case proceeding can be different against different defendants depending upon the relief sought in the plaint.
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