If defendants in a legal case have passed away and the plaintiff doesn't know their legal heirs' details, the court can be asked to direct the deceased defendants' counsel to provide this information. This is a statutory obligation, and the court will typically issue a notice to the other party upon receiving intimation of the death. You can file an application under Section 151 of the CPC to request the court to compel the opposing counsel to furnish the necessary names and addresses of the legal heirs.