Is it permissible for a father to request a division of one-third of the project he started with his money and reputation, first with one of his sons and then with another son, even though the father has not stopped working? And is that considered an injustice to the younger siblings?

A father must be just between his children in giving gifts. However, if some of the children help the father with extra effort and work, it is permissible for the father to give them a fair wage, or allocate them a salary, or a share from the factory, provided that this does not exceed what is customarily recognized for their effort, otherwise, it would be a prohibited favoritism.