Illegal occupancy on my father property.

My grandfather (father side) divided his property between his two sons in the state of Bihar.he had 2 sons and 4 daughters and they all agreed to this .my father lived with my grandmother (his mother) in the house till 1980 after which he father allowed his widowed sister to live in the house with her 3 children because they had nowhere to go and they were very poor.the property divided between the two sons as per the partition deed .they survived on my grandfather pension and monetry help from my grandmother passed away 10 years ago. my aunt has lived in the house for 28 years. and are refusing to vacate the father is trying to sell the house . my father offered his sister some money to vacate the house and they had verbally agreed to this.After we took 50% payment from the buyer ,my aunt is now demanding more money .she refuses to vacate the house if we don't agree to her demands, we have offered her money ,but she not agreeing . my question is what legal right do we have over the property and what legal does she have. ? This is extortion from her side since she is blackmailing us.can she refuse to vacate the house ,after the house registration ? what legal steps can we take to make her vacate .? does she have any legal right over the property even though she is not named in the property deed.and if she has a right ,what percentage is she legally given.? the partition deed clearly says the daughters have no legal right over the property and they have given up their share in exchange for money.they had all signed the deed agreeing to the terms and conditions. please help me with your legal advise on the matter.