What should a Muslim do with his mother who is trying to separate him from his wife through sorcery, despite his repeated warnings to her?

It is recommended to investigate the reasons for the grandmother's hostility and eliminate them through kindness and gentle treatment. You and your wife should fortify yourselves with the remembrance of Allah, recite the morning and evening adhkar, and consistently read Surat Al-Baqarah. The Prophet, peace and blessings be upon him, said about it: "Learn Surat Al-Baqarah, for taking it is a blessing, abandoning it is regret, and the sorcerers cannot overpower it." If the grandmother persists in her actions, she must be advised and warned of Allah's punishment. If that does not work, her matter should be brought to whoever has authority over her to prevent her. If there is no such person, then her matter should be raised to the ruler.