Leasehold To Freehold Property Conversation

I stay in delhi and owns a leasehold property along with my two brothers (both of them werw expired long time back). We all are orginal allottees from land and development authority Delhi. We all are staying in our respective floors, however, one of my brother had sold his floor/Share on power of attorney to a buyer and his family moved from here. Later on, unfortunately, he himself, his wife and 2 sons got expired. One of his son is still alive along with his wife and his son. My another brother who is again no more, however his son's are still living on ground floor, I am only one left who was the original allottee. My first question, can I alone apply for freehold of property are do I need their sons permission. My another question is if we apply for freehold of this property then the party who bought my first brothers floor on GPA will only be required for signature and doing other legal formalities or we require his only son permission also who don't lives here anymore.