1. Since your mother is reported to have lived and died abroad, you may not be able to get the legal heirship certificate in India, hence you may have to gather evidence about the successors in interest to succeed to the estates of your deceased mother and file a declaratory suit in a civil court in Goa seeking to declare the legal heirs/successors of your deceased mother. The proposed affidavit duly attested by a notary at UK/by Indian high commission at UK may be attached as an additional documentary evidence to prove the legal heirs of your deceased mother, before the court where you intend to file this suit.
2. You may have to produce the copies of the documents identifying the individuals namely their passport/OCI cards or any other reliable government identity card reflecting their name and educational certificates having your decesed mother's name reflected in it.
3. If you are filing a suit, it is pertinent that you are required to be present before court to adduce evidence to establish your case.