Step mother want to sell fathers property how can we stop

Dear Sir/Madam, My mother expired due to sickness hence my father got married again. We are 2 daughters and my step mother has a son. My father is having health issues, now my step mother is asking for share in property. Father has a newly built house which is worth more than 25 lakhs and has almost 4 acres of farming land. Could you please guide on equal share and daughters rights on Father's property. We both daughters are married, she mentally torture us whenever we go home and ill-treat us. Which case can be filed against her? How can we stop her from selling the house. Need justice.