All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is known that the Muslim who dies before paying his Zakah for one year or more, Zakah will be paid out of his estate before its distribution among the heirs. The deceased's guardian or heir, or the Muslim ruler (or his deputy) is the one who undertakes the task of paying the deceased’s Zakah.
Therefore, it is not permissible for you to take anything from the estate of your maternal aunt to settle your debts without permission of the heirs. Now, you are required to tell her guardian or heirs about your action. If they approved it and you really deserve Zakah, it would be fine; otherwise, you have to return the money and they would pay the obligatory Zakah from it.
For details about the ruling on adoption, please refer to Fatwa 82371.
Allaah Knows best.