Are we sinful if we do not give our father the money he asks for, knowing that he favors the children of his other wife, does not spend on us, and we spend on our mother?

There is no doubt that your father committed شرعية (Sharia-compliant) transgressions, including a lack of justice between his children and his two wives. Nevertheless, we advise you to be patient with him and treat him kindly, especially in his illness and old age, for honoring one's parents is among the greatest acts of obedience, and disobeying them is among the gravest sins. Allah has commanded kindness to parents even if they are polytheists and call to polytheism, as He Almighty said: "But if they endeavor to make you associate with Me that of which you have no knowledge, do not obey them but accompany them in [this] world with appropriate kindness." If the father is in need of money, it is obligatory for you to fulfill his needs for food, drink, shelter, and medical treatment. As for what exceeds his needs, it is not permissible for him to take it except with your full consent. The Hadith, "You and your wealth belong to your father," implies permissibility (إباحة) not ownership (ملك).