Undivided property

I have three elder brother and one elder sister. My second brother only alive. My third Brother had one daughter but she is also not alive. My Third brother son in law sell the 1/5th share of undivided property without consent of other legal heirs through will of third brother's wife. She is also not alive. There is no will from third brother or from his daughter. Questions. 1. Is it legal that the selling the undivided property by my third brother's brother in law without consent of other legal heirs? 2. Is the purchaser of 1/5 th share land has any rights to demand the particular portion of land on his preference? 3. Is other legal heirs has to allocate the particular portions of land to the purchaser of 1/5 th share land? 4. Otherwise for acquiring our land from the purchaser of 1/5 th share land, if we settled the amount of sale deed agreement with interest amount as on date will be allowable through court? 5. Under which law and section undivided property sale is legal? 6. Due to problem in EC no body will come forward to purchase our land. What is solutions for this?.