Land & property

Hi all this the property it was in the name of great grandfather, in 1996to 1997 my father and his brother mutually agreed in separating the property my father took the home where we stayed and for his brother we gave the lathe work shop(it was a rented place - but products inside the shop is owned in my father and grand father name) while getting the land we had one old house we planned to construct a new house in 97my moms parent helped in this and we got some amount for interest and we did it. In the year of 1998 my father passed away. After that my fathers brother came and he argued that he needs a partition in constructed house, but we refused it because my father and his brothers mutually agreed in separating and the properties. After that he didn't came for anything abt property. Recently in last year he passed away. Now his child and his wife has gave a lawyer notice stating that they are having a share in this property. And they stated that the rent which we are getting are belongs to them also. They mentioned that her father also helped in constructing the house but he didn't The land is situated in cantonment place from 1997 the house tax is paid in my fathers name. I need a advice what we can do. They gave the notice because the girl is studying but we also just now completed our education and started for job.