Who has the rights of property?

Respected Lawyers, I’ve an issue related my Ancestral Property. My Forefather Vidya Narayan gave a property/ building to his youngest son Prem Narayan (in 1975) which had 4 shops on ground floor and a residential flat on first floor. In the will he also mentioned that 1 shop out of 4 would be in custody of Shiv Narayan (my father and Vidya Narayan’s eldest grandson) forever and Prem Narayan has no right to ask for vacating the shop from Shiv Narayan ever. Shiv Narayan has the right to possess the shop but he would pay 20 INR to Prem Narayan as the shop rent. Prem Narayan made a will in 2004 and divided the same building to his two sons Amit and Akhil. He has another son Aditya who receive a separate property from Prem Narayan. Amit received two shops and Akhil received one shop and the flat on the first floor. There was no mention of the shop my father possessed since 1975. Prem Narayan died in 2004 and my father Shiv Narayan in 2010. Now, my mother has the possession of the shop post my fathers death and running small tailoring business for her expenses. I’ve no siblings and due to a private job I am not able to afford the full expenses of family so it is a source of income for my mother. My mother also files ITR every year. The issue is- Amit and Akhil who only have the right on 3 shops and the flat have sold the entire building on 11th March without informing or involving my mother. My question is what is the best way to take stay on the registry so that my mother receives all the rights of that shop? What points should I mention? I am firm that Amit and Akhil do not have the legal right to sell the property including my sohp. They can sell their part but not my shop. Who has the right to claim my shop? City is Kanpur, UP