OCI Collection Procedure

I have applied for OCI for myself, my wife and my son all together as a family application.

The status now shows that our OCI are arrived at London and I now need to send the original passports for stamping.

The question is should I send all 3 passports together in single post and only one self-addressed Special delivery envelope for return or should I send all passports separately?

Thank you in advance.

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