Rented shop

In the year 1987 my father took 2 shops on rent from a Mehant(priest of religion) due to which the rent amount was quite less. In year 2005 both parties agreed and had an agreement to pay certain amount to buy the shops from which half the amount was paid. Now both my father and Mehant both died in year 2012 and 2009 respectively. Now the children of mehant are asking us to vacate the shop we are saying to get the registry done and take the balance amount but they are not ready to sell the property. They agree that they have received the amount but will not sell it to us. Some background for the same case: 1. Mehant is successor to a senior mehant. And after being the legal heir he neither declared a legal heir of the property. Can his children be the heirs of the property. 2. They disagree to register the property stating that they have not distributed the property among their siblings as they are 3 sisters and 1 brother. 3. In agreement to sell the property it was mentioned that till registry we will not pay any rent to them. Still we have paid them rent till March 2018. Kindly help my mother is looking after the shop and it's the only source of income to her.