Selling of property

My father has been allotted a house by the housing board, till his death he has not cleared the installments and after his demise my mother has cleared the instalments alongwith interest to the housing board and requested for transferring the house in her name by submitting the death Certificate of my father. According to her request, the housing board has sold away the allotted house in favour of my mother and sale deed has also registred with the sub-registrar. Before getting the sale deed from Housing Board, expecting that it will be transferred in her name as there is no other claimant as she is only the wife of my father, she has written a WILL due to her old age health bequeathing the above house property in favor of her 4 sons with free will and consent without any force from any-side in sound health and mind. The written will is unregistered and notary was only made. NOW OUR MOTHER WAS ALSO EXPIRED. After 6 years of her death, now we want to SELL our House. Now we have obtained no objection / relinquishment letter from our sisters. NOW MY QUESTION IS WHETHER WE 4 BROTHERS HAS TO OBTAIN THE LEGAL HEIR CERTIFICATE OR SUCCESSION CERTIFICATE FROM CITY CIVIL OF COURT IN WHICH PROPERTY JURISDICTION COMES OR NOT NECESSARY. PLEASE GUIDE US.