Would like to have your opinion and suggestions please in order to make it foolproof

We used to stay in a rental flat in Mulund, Mumbai and the rental receipt was in my mother's name. My Mother expired in 2005. Meanwhile a Builder approached the Building tenants with aproposal for redevelopment of the flat. In March 2008, the Builder executed an registered agreement with my Father for redevelopment of the Flat, after obtaining no objections from myself, my brother and my two sisters In June 2008 my Father prepared an handwritten will wherein all my Father's assets were equally distributed amongst the four of us. All of us received a copy of the Will. In this will he has nominated me as the sole owner and claimant for the redeveloped flat upon his death. My Father's demise took place in October 2008. Meanwhile this handwrittten will was notarissed in Dec 2008. In March 2010 the Builder handed over possession to me based on the Will and after obtaining no objections from my Brother and two sisters Now I have the following documents in my favour: 1. The notarised handwritten will. 2. Possession letter from the Builder. 3. No objection letters from my Borther and two sisters dated March 2010 4. Share Certificate in my Name 5. Maintenance receipts from the Society since its inception However while trying to Sell the flat recently, the Purchaser lawyer;s objected stating my Brother and two sisters should be present during the process of registration and they should sign a NOC in front of the Registrar. This was not possible since one of my Sister is in U.S.A, the other in Kolhapur and my Brother is in Bangalore. Asking for their presence and NOC again would be like awakening some desires within them and creating a fussy situation, since the Price of this Property has appreciated substantially. In view the token amount received from the Purchaser was returned to him. MY firm belief is the above documents should suffice for any prospective Buyer. Would like to have your opinion and suggestions please in order to make it foolproof