Possession of property

My father has bought a house in the year 2012. The house has 3 floors. My father has bought a portion of the ground floor and the topmost floor. In the middle floor d previous owners stay. We have registerd d property in the year 2013. The complete registration of the top floor is complete but the registration of the ground floor was incomplete and only 2 lakhs has been paid as the token amount as agreed upon by the owners previously. The time limit for rest of the payment was given until 2016. Now there was a printing mistake in the agreement and somehow the year was mentioned as 2016 instead of2015 which neither us nor the owners have noticed before. Now the owners are forcing my father to vacate the ground floor as they are saying that they dont want to sell the ground floor. My father resisted and said that he is ready to pay the rest of the amount but wont vacate the ground floor. He has also decided to take legal recourse. But as he is a retired person and I stay outside for my job he is afraid that the owners might try to use forceful means to vacate the aforesaid portion. Kindly give me your valuable inputs regarding the same and what would be an appropriate course of action in this regard. Thanks