Illegal sale of property

sir

     my  late grandfather had a property.amounting to about 2 acres.he had 8 children. out of them one children of him had sold the entire propertywithout taking consent of anyoneand has even given registry of thewhole property.it has been done about 15 years ago but only recently we have come to know about this.

1)what should be my step now.

2)can any criminal case be made in thisregard.so that he can be punished

3)under what sections he can be prosecuted