The legal heir can very well take legal action by first issuing a legal notice to the society condemning this illegal act and instruct them to revert or set aside their act of adding the brother of the deceased owner as the member of the society and to add the name of the legal heir of the deceased as the member of the society by producing the legal heirship certificate.
Before that the legal heirs have to submit an application for this puropse and exhaust the available remedy and proceed only when there is no proper response to the application submitted.
Failing to respond, the legal heirs can file a suit for mandatory injunction against the society before the cooperative court seeking to remove the name of the brother of the deceased owner from the membership and to direct the sociey to add the name of the legal heir as a member of the society as per the law of succession.