Rights of tenant over house having possession for 32 years

we are living in house since 32-35 years since landlord family left the city they said us to live there till we want. we paid rent for first 18-20 years but since we didn't hear anynews from landlord nor did they ever visited so we stop paying rent and took care of the house like our own house.we spent money on its maintenance whenever required but suddenly we came to know few days back that landlord son had made agreement of the house with other party without letting us know and he will be visiting the place after few days.so what should we do so what should be the legal steps that we should do so that they can't tell us to leave the house or provide us the benefit for looking after house and its maintenance in their absence for such a long years.