Using Money that I send to Father for 6 years.

Hi Sir Me and my wife are salaried individuals. I have been working since 6 years and my wife since 4 years. We are filing ITR every year. My wife transfers some amount every month to my bank account . I add them to my savings and transferred amount every month to my fathers account. We are doing this since 6 years to accumulate money to purchase a home. My father withdrew that amount every month and rotated that money for interest. We want to use that money now to purchase a flat. The amount is around 20L. Can I use that money now ?. If so, how can I use it ?. Because of demontisation, I want to know will there be any problem if I deposit that money into account ?. Can he deposit that amount into my or my wifes account ? . What we should do, if we want to use that money, without facing any problems from IT department. Actually we looked for a flat(under construction) and almost ready to purchase it. The builder told that , he would accept No cash and only CHEQUE. We have to pay 20% every 4 months through cheque. Can you please help what to do under these circumstances ? P.S. My father had never filed an ITR. He has a small shop in my town. His income does not exceed 2.5 Lakhs every year.