How can one deal with a father who is suffering from symptoms of sorcery but refuses to acknowledge it or seek ruqyah, especially given strong suspicions that the grandfather performed sorcery on the family?

We advise the questioner to consistently recite the prescribed invocations for seeking refuge and the lawful protective incantations, and not to accuse their grandfather of sorcery or of seeking help from sorcerers. Sorcery can be treated with lawful Ruqyah (definition) (Islamic exorcism), and it is permissible to perform Ruqyah on the father without his knowledge, because the important thing is to deliver the Ruqyah to the patient, and there is no fear of harm from it. One of the best ways to deal with harm from relatives is to maintain seeking refuge [in Allah], to fear Allah, and to be patient in the face of harm. For whoever fears Allah and is patient, the scheming of others will not harm them. Respond to ill-treatment with kindness and beautiful patience, as Allah the Almighty says: "And not equal are the good deed and the bad. Repel [evil] with that which is better, and thereupon the one whom between you and him is enmity [will become] as though he was a devoted friend." (Qur’an 41:34). And whoever does that, it is as if they are feeding them hot ashes [a metaphor for humiliating them by their good deeds], and they will always have a supporter from Allah.