Is a father considered unjust to his children from his first wife if he transferred ownership of the marital home—which was all he owned—to his second wife through a sale and purchase 20 years ago, in exchange for her spending on him and their daughters for 10 years after he lost his money and job?

It was not obligatory for your mother to spend on herself, her husband, and her children, and her volunteering with the people [or with provisions] was an act of charity. As for what the father did by selling the apartment in exchange for her spending on him for the duration of his life, this is an invalid sale due to the ignorance of the price, and the apartment shall be returned to the heirs. The mother is entitled from the inheritance to the amount she spent on your father. If a dispute arises among the heirs, its resolution lies with the Sharia judiciary.