Pension, proverty,job

Sir,my father expired 3months back.he was working as TN SI of police.He is from well stood family.He was addicted to drinks, cigarette.He died due to liver failure.He did 1st marriage in Kerala 1988( having 1daughr married ,havng 1kid they are completely in Kerala). He cheated my ma and married her registered @Chennai 1990.I m the only daughter for them.I also married recently.My dad was living with us completely ard 27+yrs.His police service book, other nominations are me and my ma.He dint devorced his 1st wife ( she was also legally married other than marriage certf they don't have any proofs because my dad lived with us oly not with them but he used to giv some amnt for their living ard3L he gave for that 1st daughter marriage we have proof on it) .Now my dad's first wife, his mother filed petition askng for his pension. Sir, we only taken care of his entire medical expenses about 20yrs he was continoualy hospitalized & recovered due to his drinking habits we have all those medical records.His parents, siblings,1st wife never ever came to visit him & helped us, now they all want money.They are harassing me , my in laws thr msg,calls , petitions.please let me know whether his mother have rights on his pension etc.Can I file a case against them.