How to document a registered promise note with own terms & conditions?

My brother want registered promise note from my mother that' after giving her half amount of my dad's property, my brother will not take any responsibility of mother and all sister will look after her. My father was the first holder of the property and second holder is my brother that too my brother hadn't invested in that property and my father hadn't made any nominee. So in short my mother name is not mentioned anywhere in the property agreement. He agreed to give half amount of the property to my mother but the condition is he want registered promise note so that my mother won't able to claim anything in future. Please advise how to make that document and what will be the cost or is there are any other Legal way so that my mother can get her property..