Is it obligatory to inform the person who pays sorcerers to harm the questioner and his family that their sorcery has succeeded, while reminding them of the torment of the hereafter, or should they be left to their own devices?

Accusing people of sorcery is not permissible unless the accused admits it or trustworthy witnesses testify to it. This is because visions and suspicions are not a justification for accusing an innocent person of this heinous crime. Allah Almighty says: "And those who harm believing men and believing women for [something] other than what they have earned have certainly borne a slander and a manifest sin." If you become certain that what afflicts you is sorcery, then seek help from Allah and strive to perform ruqyah on yourself. If you become certain that someone has bewitched you, either by their admission or by the testimony of trustworthy witnesses, then advise and warn them.