What is the method for dividing the inheritance of a woman who passed away, leaving behind a mother and female siblings, given the presence of her adopted son, and how should the money that was a trust with her be disbursed?

Adoption is not permissible in Islam, based on the words of the Almighty: "And He has not made your adopted sons your [true] sons. That is [merely] your saying by your mouths, but Allah says the truth, and He guides to the [right] way. Call them by [the names of] their fathers; it is more just in the sight of Allah. But if you do not know their fathers, then they are your brothers in religion and your protectors." Therefore, an adopted son does not inherit from your female cousin, nor does he have any right to her estate or to be attributed to her, unless she made a bequest to him not exceeding one-third [of her estate]. The woman's money must be given to her legal heirs (her sisters and mother), and the adopted son has no relation to the inheritance. Matters of inheritance are serious and complex, and a mere fatwa is not sufficient; rather, they must be referred to Sharia courts for investigation to establish rights, debts, and bequests.