Is it permissible to take from the jewelry and personal belongings left by a deceased niece, or to dispose of them as charity, or do they constitute an inheritance for her four brothers?

All that the deceased left behind is considered an inheritance and is to be divided among her heirs. The mother is not permitted to dispose of any part of it—including what the deceased gifted her and what she possessed before her death—except with the permission of all the heirs. It is not permissible to give charity from the estate on behalf of the deceased unless all mature, adult heirs grant permission. The mother's sale of the two gold earrings is considered an unauthorized sale, and the heirs have the option to ratify it and take the price, or reject the sale. The inheritance must be distributed as Allah has ordained, after identifying the heirs. The full siblings (two brothers and two sisters) receive shares such that the male gets the equivalent of the share of two females, provided there are no other heirs: "And if there are brothers and sisters, male and female, then for the male is the share of two females. Allah makes clear to you, lest you go astray. And Allah is Knowing of all things" (An-Nisa: 176). It is preferable to refer matters of inheritance to Sharia courts or consult with knowledgeable scholars, due to their seriousness and complexity.