Tenants already staying, need to build another room.

I have a property and with that TWO different tenants. One is living with us for 30 years. Another is living for 15 years. I have a son, recently married. For them, I need rooms. They currently stay in 2nd floor (top floor) which is like a hall room. One room, one baranda, one bathroom. In Winter, the room gets very cold at night and in summer, its like a micro-wave oven as its a top-floor with glass windows. For these I need to vacant my tenants which they refused.

Now, both the tenants bought their own flats in the same city that of mine. One is living their own flat, but kept a servant in our room. Another is living in our room, but put tenant in their flat. Please suggest me how do we progress? What is our chance? How long approximately will it take? My main concern is that, they will claim that we do have extra room so our requirement is not valid.