1. What you are doing is absolutely wrong
2. you will need 3 people - 2 witnesses and 1 person who will sign on behalf of your grandmother. This person has to specifically endorse on the Will that he is signing on the Will on the directions and instructions of your grandmother since she is not in a position to sign due to her old age as her hand shivers while signing. The same endorsement can be made on the Will by the 2 witnesses. Additionally your grandmother can put her thumb impression on the Will and all the 3 persons will have to state and endorse that they have seen your grandmother putting her thumb impression on the Will
3. let any of the above three persons either type out or write the last wishes of your grandmother on the Will paper. the person typing or writing can again endorse and state that he has so typed or written down the wishes of your grandmother
4. the Will has to be drafted in the same manner in which your grandmother dictates. that will correctly reflect her true intentions how she wants her property to be dealt with after her death
5. so dont make any back dated paper. if your grandmother can speak and understand what she is speaking then let her only dictate what she exactly wishes
6. what you are trying to do is in a way illegal