What is the ruling on zakat for an inheritance after the father's death, if it has not been paid for 6 years, and there is a minor involved, and can waiving a portion of the inheritance be considered as zakat?

The matter, dear questioner, is as we have stated: the obligation to pay zakat before the division of the inheritance. The presence of minors among the heirs is not a justification for not paying zakat. You can all testify before that council that your father had unpaid zakat, so that the value of the zakat is deducted from the inheritance and from the share of the minors. If the council refuses to do so, then each one of you must pay what reached his share of this zakat, and your father will bear the consequence of his negligence.

What you mentioned about wanting to waive a portion of your share for your stepmother and sister as zakat for your father and his daughter is not valid because zakat cannot be paid to those whose maintenance is obligatory upon the zakat payer, such as a wife and descendants. Therefore, it is not permissible to pay zakat from his wealth to your stepmother and his daughter.

The real estate that your father owned and resided in does not require zakat on its value. Similarly, the real estate that he rented out does not require zakat on its value; rather, it is obligatory on its income if it reaches the nisab (minimum threshold) and a year has passed over it. As for the closed shop, if your father did not acquire it for trade, meaning he bought it to rent it out and not to sell it when its price rises, then there is no zakat on its value. But if he bought it to sell it when its price rises, then it is subject to zakat as trade goods.

Similarly, regarding the lands he owned: if he bought any of them with the intention of cultivating them or building on them, there is no zakat on them. But if he bought them with the intention of trading them and selling them when their price rises, then zakat is due on them. Perhaps it is best for the questioner to directly consult scholars regarding these issues related to inheritance and its past zakat, as they are complex matters that require further clarification and detail.