Is the zakat on gold calculated based on its price at the time of purchase or its current price, and do sisters share in the zakat if they benefit from the gold later?

If a mother acquires gold for adornment, there is no zakat (definition) due on it according to the majority of scholars. However, if it is not for adornment, then zakat is obligatory on the mother alone. The principle is that the zakat on gold is paid from the gold itself, but if money is given instead, then its value at the time of paying the zakat is what matters. As for the gold gifted to the sisters, if it is for adornment, there is no zakat on it. But if it is for other purposes, a new hawl (lunar year) begins for it, and its zakat is to be paid after its completion, provided it does not fall below the nisab (definition) (minimum threshold).