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There is no legal requirement that the family be told of a relative's death. Likewise, a non family member can register the death without the consent/knowledge of the family.
We do not know of course whether your Mother has made a Will, but if she has, it will be up to the Executor named in the Will to deal with her Estate in accordance with ht eterms of the Will. If no relatives are mentioned in the Will, it is unlikely the Executor would make contact with you.
I hope this assists and sets out the legal position.