Will deed on white paper is valid or not

My brother-in-law has expired 5yrs ago ie. In 2014. He had no children. He is law graduate from Osmania University. He has retired from TSSPDCL. He owns the house on his name. and flat on his wife name. But he lives in the flat and house has been constructed afterwards. In the 1St floor two portion exists. One portion has given to rent and the other has been given to her sister without rent being poor with low income. And his sisters husband is a practising lawyer with his with another senior lawer. With the help of a senior lawer and collision of 2 lawers a fake, forgery will deed not registered has been created after 1 year on his sister's name on white paper with 2 witnesses. And my question is whether this white paper will deed is valid. How ţo vacate. He is forged the will deed and a case has been filed. We had given reply. We have not filed any forgery case so far. My sister wants this property back. Actually we want file cases against 2 lawers. My sister wants to get back the property. Kindly advise.