Father's property

Hello sir/mam my wife's father expired few months ago.he had a self earned property of about 20-30 cr. He had three daughters and one son(X) who is a lawyer too and wife. Recently his son is asking his sisters ie my wife and her two sisters to sign the documents regarding some case related to the house in which he is residing. Those documents contained a descripttion of a Will which was not in the knowledge of my wife, her married sisters and my wife's mother too. Will stated that the property belongs to his son and there's no share of the daughters in any house property. ornaments etc. Although his son has to pay for mother's living and medical expenses.There is a signature of my wife's father in that will but my wife and her sisters and even the mother do not believe that will is real and confident that the signature is also fake though they dont have any proof of their father's signature. X told that the will has been written 3 years ago wihout the knowledge of My wife's mother. X has made all daughters to sign in the documents related to give special power of attorney to him for the case. Now what should be done?, can my wife and her sisters file a petition...what would happen after filing the case..