Is zakat obligatory on the embezzled money that multiplied after being invested by the embezzling brother? And does he bear the sin alone, or do the heirs share in the sin? And how is zakat calculated for past years, given the dispute among the heirs regarding the obligation of zakat on the embezzled money?

If stolen money is recovered, it is subject to zakat (definition) for one year upon its recovery, as it is considered like a debt owed by an insolvent person. This is the most equitable opinion. Zakat must be disbursed before dividing the money among the heirs, because zakat is a debt that takes precedence over the rights of the heirs. After the division, each heir examines their share; if it reaches the nisab (definition), they start a new lunar year (hawl) from the day they receive it, and then pay zakat on it.