Can a man inherit property of 2nd wife claiming to be her Class I heir, if the 2nd marriage is void?

A man legally married in year 1967, without divorcing his first wife, starts living in with another woman whom he considers his second wife. He lives with both wives during his lifetime, and the first wife does not object to this arrangement. In public records of the second wife as well, she uses his surname. He does not have any children from both marriages. During the life time of the second wife, she acquires both immovable & movable property in her single name. In her movable assets in bank, she puts the name of her husband as nominee. Now as per Hindu Marriage Act, a second marriage with previous married wife is null & void. The only blood relation alive of the second wife is her sister, as her marriage is null & void as per Hindu Marriage Act. Second wife dies intestate. Now after the demise of second wife, the man claims to be her only heir (Class 1 heir under Hindu Succession Act) & illegally gets immovable property transferred in his name. & bank accounts, deposits also he gets transferred in his name as he was the nominee as her 'husband'. Upon demise of the husband, the first wife is now claiming rights to all his property, even the property he illegally acquired from his second wife claiming to be his sole legal heir. Now the Hindu law does not recognize a second marriage. So the husband could not have inherited the property of the second wife. However due to over sight of legal authorities, he got it transferred in his name. What are the legal options of sister of second wife? Does she file letters of administration or does she file criminal case for fraud ?