1. IF the names in the Share Certificate /Demat Holdings are those of Father and his Brother, THEN legally it will be construed that Father & Brother each have 50% right /stake on such Share Holdings.
2. Serve a Legal Notice /Caveat to the "Indian Co." restraining them from making any type of Transfer of said Share Holdings.
3. Since Father has not left any WILL document, file a Civil Court case for directions to transfer the Father's share holding (50%) in name of Mother. Nothing is "automatic" in law and due procedures of law must be followed.
Keep Smiling .... Hemant Agarwal