PROPERTY SOLD BY LEGAL HEIRS IN VIOLATION TO THE WILL

My grandfather's brother has recently expired .He is having a wife and one mentally challenged child. Before his expiry he has written a registered will. In the will he has written that all his assets are divided in to two parts and that myself and my brother has to take care of the said assets till the lifetime of his child. He has also mentioned that no one can sell the property till the lifetime of his child. Only after the expiry of his child, me and my brother can enjoy the property. However in violation to the will , after his expiry his wife and my brother had sold a portion of the asset which is given in my name. Now they are planning to sell all the assets whichever given in my name. I have already issued a legal notice to all the subject parties but there is no response. What course of action I can take to stop them from selling the property. If I file a case in court to cancel the sale transaction and to take stay order for remaining assets, what court fees I have to pay?