Property possession

My wife received one property of 6 decimal with eastblishment of 940 sqft 2 storied building via gift deed from my mother in law. On 2016 September. When the sattlement done with father in law he agreed and signed as a witness in our deed. Adjecent to my possession building father in law's building is there which was joint in first floor and 2nd floor by cantilevered. When the sattlwment done with father in law he blocked the cantilevered part permanently by brick works. Now after measurement of land it is found that our some portion of construction laying in his area. He demanding that part. Nowy questions are? With construction possessed land less than 6decimal by us. We are using and that part of construction by staying in 1st floor and 2 nd floor and giving by rent the ground floor room. Shall have to leave the possession of that part which he demanding?