How can one deal with a father who favors his second wife and her children, while treating his first wife and her children poorly and differently, and what is the explanation for the possibility of magic affecting his behavior?

You must be patient and kind to your father's wife, out of dutifulness to your father and because kindness removes animosity. You must also not neglect your studies or duties. Your mother must be patient and fulfill her duties towards your father. It is not permissible to accuse your father's wife of sorcery without proof. Allah says: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin." (Quran 49:12). You can persuade your father to perform Ruqyah (definition) (Islamic exorcism) and to recite or listen to Surah (definition) Al-Baqarah, for the Prophet (PBUH) said: "Recite Surah Al-Baqarah, for taking it is a blessing, and leaving it is a regret, and the sorcerers cannot overcome it."