Unfortunately it is again it has once more came into light of the ill-practice of advocates preparing fake divorce deeds in Mumbai/ other parts of Maharashtra, the wife may or may not be a victim of this trend depending on how aware she was about the fake divorce decree. If the same was hidden from the husband at the time of marriage he is a victim of cheating and fraud.
Yes your brother in law can file FIR under 495., 495, 420, and 405 of I.P.C..as the marriage is a contract.
494 Ipc -
Marrying again during lifetime of husband or wife.—Whoever, having a husband or wife living, marries in any case in which such marriage is void by reason of its taking place during the life of such husband or wife, shall be punished with imprisonment of either description for a term which may extend to seven years, and shall also be liable to fine.
495 Ipc-says -Same offence with concealment of former marriage from person with whom subsequent marriage is contracted.—Whoever commits the offence defined in the last preceding section having concealed from the person with whom the subsequent marriage is contracted, the fact of the former marriage, shall be punished with imprisonment of either description for a term which may extend to ten years, and shall also be liable to fine.
2. The Marriage can be declared null and void and your brother in law should move a petition for that within one year of knowledge of its existence. DV case will stand if facts of cruelty/the allegations are mentioned and if it can be proved .even if the marriage is void DV case can be filed.
3. Divorce can be file on nullity ground. However nullity order or the ground for filing nullity will not dismiss her claims of maintenance or other reliefs if she can prove it in court .
Cheating, harassment, fraud will be applicable if the husband was not aware or seen the so called decree made by the advocate