Disputed Property

My Question is related to dispute created at one of our maternal property. One house was on the name of my Late maternal grandmother. She had 5 children (3 female & 2 male). As House was on the name of Maternal Grandmother so, all 5 children have right in the property. Her eldest son was living in that property but unfortunately he has been tortured by his son and daughter in law. So they left the house. Due to bad condition of eldest brother, 3 siblings are ready to sell the property but one refused. My Mama doesn't want to give his part to his son so he along with other 3 siblings voluntarily named their part to the youngest sister. Now, 80% property is on name of one sister (my mother) and 20 % is on the name of another brother who doesn't want to help. Currently my Mama's son and daughter in law are residing there. Now we want to sell my mother's 80% share and give money to Mama because he does not having any money left with him to live life. but due to rest 20% share issue, we are not able to sell legally. Can we sell the property in dispute. Property cost is 30 lakhs but in dispute we are getting only 10 lakhs for 80% share of property. If we sell our 80% share in disputed property than can 20% share brother object or file any case against us? And if we want to go in legal ways what can be done in this case. How much money and time it will take to resolve.