بسم الله الرحمن الرحيم
(Fatwa: 947/920/SN=8/1438)
In the question mentioned above if that mad sister dies then her alive sisters and uncle shall be the Shariah heirs. If at the time of her death, two or more sisters whether three or four sisters would be alive then the sisters shall get two third while the rest one third shall go to the uncle.
Note: It is a principle rule. When a man dies, who dies first and who later it is not known. Thus, when the mad sister dies then you can write the details of the near and distant relatives who are alive to know the Shariah ruling.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband
