my mother property, can she have it if no one to claim

Hello Sir, I need your advice, how can I help my mother to get back the property on her name. My grandfather(narayana) deceased 30 years back. My mother has only one younger sister. As per hindu costumes her cousin brother (Ram s/o Dasharath) have fulfilled the rituals. As of now Ram and Dasharath both are deceased and Dasharath sons are enjoying the benefits of the property. My mother and her sister wanted to register this land on their name, I wanted to know what kind of no objection certificate is required from the current sons of Dasharath before submitting affidavit to get legal hire. We wanted to take signatures on stamp paper from all the sons of Dasharath, to avoid any future disturbance . Kindly suggest