advice on house property will issue

1) We have a house which is in my mothers name. Now my mother want to make a will that after her death this house will be mine and my brother and sister will give N.O.C / no claim affidavit in the court that they have no right in the that house which my mother is transferring in my name after her death ( making a will). I would like to know , can my brother and sister take that affidavit / N.O.C back and make it null & void even after the will is made and claim right in property OR once the N.O.C is registered in court no change can happen in NOC. That is during my mother lifetime 2) And is that NOC / affidavit can be made null and void after my mothers death. Please advice thanks