How to deal with Landlord

My father in-law along with his brother rented a property some 50+ years ago. There is no proper agreement, only rent receipt was issued in his brother's name. Uncle with his family (Wife & son's) shifted to new address and then after my father in-law along with his family is staying in that house. But receipt for many years is issues in Uncles name only. From past few years landlord dint issued receipt hence father in law stop paying rent. Now landlord want us to evict for which legal notice was shared saying Family has illegally occupied the place hence pay the balance rent and leave. We have replied the notice. Now we have senior citizen in house (In laws) and there is no toilet in house. Common Toilet is bit far and unclean. Due to health issues they are finding it difficult to use it. Also the building needs a huge repair and construction is very old (60+). How to deal with this issues We have approach landlord and requested for repair/redevelopment but he is not ready We also stated that we are ready to pay rent but pass receipt and do repair