Dear Querist
My opinion on your queries are as under:
1.Is the will valid after her death?
Opinion: yes, the Will shall be valid after her death and if registered then nobody can challenge.
2. Other better possibilities like gift deed without NOC from daughters? anything else?
Opinion: there is no requirement for any NOC from her, your grand mother is the absolute owner of the property and has all rights over the property, nobody can restrain her to use her rights.
3.She has included my Name on her Ration Card from my birth , does the transfer of property tax, water tax and payment of it for particular number of years , give me an upper hand or any legal rights?
Opinion: yes, it will be.
4.Any way with Power of Attorney or Mortage it on my Name has a legal chance?
Opinion: no need to worry, Will is sufficient. After registering Will it will be better to published the same in newspaper and save those papers which will be helpful in future when she will tried to challenged the will in the court.
Feel free to call