Is the value of the estate of a father who passed away 20 years ago calculated based on the original shop he left behind, or on its continuous growth and development over these years, especially since one of the sons took over its management and developed it for himself?

There is no problem in dividing real estate among heirs according to the Shariah division. If its division is not possible, it should be sold and its price divided among them. As for the income from the commercial shop, its details are not clear: Is the capital used in it shared among the heirs or specific to your brother? And was the expansion done with the heirs' money or his private money, and with their permission or not? All of this affects the answer. Therefore, the matter should be referred to the Shariah court or to a qualified scholar of jurisprudence to hear all parties and determine how the profit should be divided.