How to defend second marriage is valid?

Hello All, My aunt is stuck in a situation where she is not aware how to proceed, please help her out with your valuable suggestions. Thanks in advance. My aunt is married to a person 'A' in 2002. Came to her mother's home after 2 months of her marriage after knowing that he is cruel. After waiting for 4 years i.e., in 2006 in-front of the gentlemen of the village they (my aunt and person 'A') have parted ways with agreement signed by both parties. And till now she was not aware of the whereabouts of the person 'A'. After waiting for 8 years i.e., in 2014 she got married to another person 'B' without taking divorce or filing petition through court. For Person 'B' it is a second marriage and has two children, and his first wife is not alive. While marrying the second person 'B', my aunt and her family gave all the information about her first marriage including the agreement made between my aunt and person 'A'. Person 'B's family and mediator were also aware of all the facts before getting married to my aunt. Now after 6 months of my aunt's second marriage, person 'B' has filed a case saying that the second marriage is void and my aunt's family gave false statements while getting married. Person 'B' says he doesn't like my aunt and marriage is not valid. Note: Person 'A' now also got married to another lady and has two children. So, please find my questions below: 1. Is my aunt's second marriage void, even though she is being deserted by her first husband for 8 years? 2. Knowing all the facts, person 'B' has married my aunt and now says it as void. Can we file an adultery and 420 cases on him? 3. How do my aunt defend the case filed by person 'B' that the second marriage is a valid one? My aunt is in such a worst situation as now she is not accepted by person 'B' and can't go back to person 'A' who is cruel. Please help her. Thanks a lot.