My father second marriage

My father on 28/10/2020 told my mother, me and my sister that he is married to another lady from past 5 yrs (2014-2015) . He didn't gave divorce to my mom neither he is willing to do, means technically he did bigamy which is not legal as per hindu marriage act. He repetitively says that he is not willing to leave any of his wife's.. He is an sbi employee ( new delhi, main branch) , of 55 yrs of age, has 5 yrs of job left.. I am 28 yrs old female and unemployed.. My mom is 52 yrs old and an housewife. She us financially dependent on him and has no property of her own.. My sister is in 12th class.. In 2018 we bought a property of our own in noida extension . Property is on the name of my mom and dad both.. Possession of property is due on july 2021 and my father has a loan to pay on his head which he might end up paying in near about 20 yrs from now.. We need help!! Please somebody suggest what step should my mom take now?? My mom dont want to set him free by giving divorce but she want her rights.. Be it property.. Be it pension money.. Please guide us further in this direction..