Crpc 494 bigamy act

Sir My friend and his wife married on March 2011. Both are Hindus, bank employees and different castes. My friend wife family based on her income and advised my friend to sacrifice one salary to her family. This was not accepted by my friend. After that too many issues raised. My friend wife lodged a false police complaint against her husband stating that he is having illegal affair with her maternal aunt unmarried daughter is the main cause and other irrelevant issues like Dowry, beating, abusing etc in 2014. All are false . But Lower court punished him only under 498A for illegal intimacy with her sister in 2018 with her relatives influence i.e., court superintendent is her relative. After that he appealed the judgement in sessions court and acquitted from the 498A in December 2019. After that he filed divorce petition in sessions court in February 2020 and it is still pending. My friend wife tortured her sister with the lower court judgement. She is sending unknown letters nor communication to the bridegroom address with that lower court judgement. My friend wife sister decided to live in relation with my friend in 2020. He too agreed for the Same due to his father health. Now my friend and his wife sister got a baby. Baby birth certificate is with my friend wife. My friend and his wife sister not married. My question is, is it punishable offence under law. My friend wife decided to lodge Bigamy case against them. In this case pls suggest any tips favouring my friend. All are Hindu. My friend wife also lodged DVC case against him and his father and mother in 2016. His father died in 2021. DVC case also not disposed. Case is at cross examination of his wife. By using baby birth certificate, is there any chance to turn DVC case against to my friend and any protection before filing of Bigamy? Kindly suggest how to overcome it.