Is it permissible for the eldest brother to intervene and purchase the commercial store for an amount less than its market value in order to divide it among the heirs, knowing that there is full consent among the siblings and recognition of the eldest brother's effort in establishing the business?

It is permissible for the eldest brother to purchase goods and equipment for more or less than their value if all heirs agree to it, because the wealth is theirs and they have the right to dispose of it with their consent. This is not usury (riba) because he is buying goods, not a deferred monetary debt for immediate cash. It is permissible to sell shares that include debts, cash, and tangible assets if they are mixed, as in disinheritance (mukharaja) and the sale of company shares. Therefore, if the mentioned amount is the value of the company with its assets and debts, there is no harm in purchasing it for 200,0 or less. However, purchasing debt with cash is not permissible.