Is the son sinful if he does not visit his sick father—whom the other children expelled the son from his home and prevented him from seeing his father—or is it obligatory for him to strive and exert effort to see him?

What your brothers are doing by preventing you from visiting your father and accusing you of witchcraft without proof is a reprehensible act, an injustice, and a severing of family ties. We advise you to strive for reconciliation between you and them by involving wise relatives or righteous individuals to speak with them, clarify the wrongness of their actions, and emphasize the obligation of brotherly rights. If reconciliation is not achieved and you suffer harm from visiting him, then you may cease visiting him and maintain kinship ties through other means you are able to, such as calling, corresponding, or fulfilling his needs, while also supplicating for him.