Legal heir certificate

We have some property in tamil nadu which is my grandfathers seif acquired property. he deceased few years ago without leaving any will. MY Grandfather ____ / \ First wife Second wife (Deceased) (Alive) ____ _________ / \ / I \ Son Son Son Son Daughter (Dead) my grandfather had his second marriage during my grandmother was alive. Now in the legal heir certificate my father ( first wife son) has included his step mother name in legal heir certificate. because of that she is not letting to divide the property from past 6 years. so from past 6 years my father is taking care of the agricultural property. before that from my grandfather's death, the second wife second son had taken care of the property for 5 years. till now they are not letting to divide the property. Now they wanted us to sell the property before partition for which we agreed. As her name is first in legal heir certificate, they tell we have to transfer all the property to her name first. Now we got to know that they are planning to transfer the property to their name and to betray us... from past 6 years my father is asking them but no good things happened till now. she also scolds the ppl who come to work in our land. and also us ( My mom, me and my sister) that we are doing prostitution to earn our daily needs. Is there any way to get affidavit and get her name changed in legal heir certificate.