Gift Settlement

Hi, My Father written will to my mother. The property is my fathers own not from his father. After my father died my mother written will to me and registered. After 8 years when she became sick one sister (actually I have two sisters) took her to her place and given treatment in hospital. But due to negligence of Hospital her condition became worse and she was above to die they brought her to me and left. I took her to chennai for better treatment and her general condition is stable now. But still undergoing treatment and she is bed ridden now. Before leaving my mother at my place they took all her gold and cash and they have also written the only property we have that is house on their names. This thing recently I came to know and my mother agreed. She did Gift Settlement to me now. But I came to know that she can cancel again the Gift settlement. Lawyers said that it is not possible to cancel Gift Settlement alone and both parties should present. But when I inquired sub register friends they said that Gift settlement can be canceled by sub register and one can fight it out in court. My query is, is there any precautions I can take so that they cannot cancel the gift settlement. f she write any will now is that will valid? Can I sell the property to my wife? If I Gift Settlement the property to my wife or son, can my mother cancel her Gift Settlement? If I take loan on the property can my mother cancel the Gift Settlement? The property is in Andhra Pradesh state. Please Advice. Thanks & Regards