What is the ruling on two brothers taking money from their sister without her knowledge, and is it permissible to disinherit the youngest brother and not repay his loan, under the pretext that he took a lot of money from his sister?

This story involves violations of Islamic law, as a neighbor is entrusted [with goods/property], and it is impermissible for him to betray the trust or squander the wealth he was entrusted with by allowing anyone to take anything from it. Similarly, the brothers' collusion with the neighbor is unlawful. All of them must repent to Allah and return everything they took from the woman's wealth without her permission to her estate, so that it may be divided among all her heirs, for the Prophet, peace and blessings be upon him, said: "The hand is responsible for what it takes until it returns it."

If the younger brother denies what was mentioned, then the claimant must prove it with legal evidence; otherwise, it remains merely a claim.

If the elder brother admits that he borrowed five thousand from his younger brother, and the younger brother denies that it was from his deceased sister's money, then the elder brother must repay what he took to its owner, unless it is proven that it was from the estate, in which case it should be returned to the general estate.