oci application

[BND]

Hi

I used to hold indian passport,which i surrender when i gain british citizenship. my husband has his british passport since a long time ,he doesn't remember what did he do with his indian passport, he has certification of registration (1993), i guess that time he gain his british citizenship. Can We both apply for Oci ? he hasn't got surrender certi or old/cancelled indian passport, would that certification of registration be enough ?
and our son,born in uk, british passport holder, can we apply for oci for him together or we have to sort out our card first?

need your help desperately.

Thanks