I have brothers

Q: I have a ninety year old maternal aunt. She possesses pieces of land, real estates and properties that she inherited from her deceased husband. Yet, due to her old age, she can not dispose of these properties that are forcibly taken over by both her brother and the children of her husband from another marriage. She has been provided for by this brother of hers, who has used some of her money and properties for 15 years, then he has expelled her, where she has settled with my mother who does not have anything, and I support my mother financially. This brother of hers is extremely arrogant and does not give her out of her properties enough money to even afford a box of medicine, which compels me to contribute to support her financially as well. Even the apartment where she lived, was forcibly seized by them. After family negotiations that extended for five years, we failed to convince her brother and the children of her husband to give her anything more than the very little that is being given to her every month, which does not suffice her basic food needs. She has been living with my mother for the whole of the period of these five years, where I provide for her after her brother refused her living with them and to increase the monthly payment given to her out of her properties. We have tried to negotiate with them to sell part of the agricultural land (Part No. 10; Page No. 61) she owns to spend on her but she refused because of her old age and lack of good awareness of life. Some of her brothers inheritors also refused, whereas some of them agreed. Finally, we found out that this solution may result in family sedition in addition to the impossibility of selling, since she, who is the owner, refused due to her old age and lack of awareness. Now I have gotten annoyed from her many requests for clothing, food and medicine. It suffices me to provide for my mother, my disabled brother, and my wife and children, knowing that she does not have any offspring and she lives in Egypt, her properties are in Egypt, and all of us are Egyptians.The question is: Is it permissible to count the money I spend on her from my own money to be out of the Zakat due on me? It is worth mentioning that she is in fact richer than me, but her money and property are not at her disposal but are seized by her brother, and that I have the money of Zakat due on me that suffices her. Is it obligatory on me according to Shari`ah to support her financially? Is Zakat not permissible in this case? Please note that I may not inherit from her if my mother dies before her. My mother's health is deteriorating more than her. Please, advise me, may Allah reward you with the best!