We had one flat in Surat in suryanagar society near sahara darwaza. Flat owner was my mother and my

We had one flat in Surat in suryanagar society near sahara darwaza. Flat owner was my mother and my mother had given power of attorney to my father. At that house my cousin brother and his wife used to live and we live in one of village of Haryana. Few days back we came to know that my cousin brother sold property to his wife and his wife sold property to builder and grabbed all money. My cousin brother used my father's voter id card, he pasted his photograph on it and showed that he is my father. Now pls suggest what can be done. How i can file case against him and his wife. What punishment can be given by court to them Pls suggest. And how we can get our house back..builder has demolished whole society and planning to build new society. Their is no even a single flat left there. And we came to know all this after 10 years. He did this fraud in 2012.