Blocked access to property

I have been living in my ancestral house which is 100yrs old. The problem is that that we are in a landlocked area boarded by 2neighbours. To the north by a house and to the east by a cooperative society. We have been using both the ways since more than 40yrs. The problem is that both the owners are now denying access to our property. The builder during construction had given an undertaking to us stating that the traditional access shall be maintained for our family and a clause would be imposed on d building owners to maintain the same. The town and country authority also had given a letter to the society telling the builder to maintain the traditional access. However now the chairman says that the society has been transferred and the builder has no say in it. Also the watchmen has been told to not allow us to enter through the society. On speaking to the builder who inturn spoke to the chairman of the society who said that they will not allow us to enter and say to go to court. The second part is that the plot is in the combined name of 4 family members who are living separate lives and I would like them to contribute to the litigation charges too equally. Your advice would be highly appreciated.