Settlement of Death benefit of deceased government employee

My mother died when I was barely a few months old. Her maiden name was Ramdevi but after merriage my father chose a different name for her, Suman Devi. But when I asked municipality about her death certificate few days ago they told me that your mother's name, as in our record, is Ramdevi. Shortly after my mother's death, my father remarried another woman, and chose the same name for her 'Suman Devi'. After my father's death in 2015, my step mother taking all death benefits in the name of 'suman devi' as in my father's service record. And the government is giving her these benefits considering Suman Devi to be alive and I am her son. In reality that's not the case. My father had 3 kids with my step mother. In death benefits availing formalities, she claimed to be my father's only wife and having 4 kids, including me. No where, she attached my mother's death certificate and sited her remarriage. She has taken her identity. Before marrying to my father she left her former husband without a divorce. She was not legally separated with her ex husband. Is her remarriage with my father legal? Now they all have taken over everything. Any help to teach them a lesson?