Name change in rent bill

Hi, We stay in rented house for last 35 years & rent bill is in my fathers name. Now my father expired on 2019 & there are some previous due as the landlord expired & no one has the authority to collect the rent. The landlord family is huge (many warisan) & stay in joint family. Now as per mutual discussion with two elder member of their family we started to pay the pending amount & two person are signing the rent bill. That time my father is alive. Now after the death of my father we requested to collect the payment but they refuse to take. Now they are asking to pay the pending amount but the bill will be given in my fathers name. We asked to change the name in my mothers name, but now they are telling they will create new agreement along with new rent amount & also will charge huge advance. We agreed to increase the rent amount but others conditions are not acceptable. We have checked in Property Tax that the house owner name is their Grandfather Name and Only one son was authorized as a collector who is no more. Kindly suggest what to do.