Is bequeathing all gold and jewelry to one of the nieces permissible in Sharia, given the existence of other heirs? And is there any injustice in that towards the husband who kept the gold? And how should the inheritance be distributed if that becomes obligatory? And is Zakat obligatory for all past years, or should it be paid once upon receiving the money?

A will is not proven by mere claim, but by evidence or the heirs' affirmation. If the will is proven, you have no right to what your paternal aunt willed except within the limits of one-third of the estate, and any excess depends on the heirs' approval. Her will is valid within the one-third limit, and she is not obliged to be fair between her brothers' daughters. The willed property becomes yours upon acceptance of the will, and zakat is due on it annually, once a year has passed since its acceptance. If the heirs are the husband and five sons of a full brother, the husband gets half, and the remainder goes equally to the sons of the full brother, and the son of the full paternal uncle gets nothing.