Is not visiting relatives for long periods or not visiting some of them at all considered a severing of kinship ties, and does this prevent healing from a chronic illness, or is the cause of the illness the father's involvement in usury, and is the son held accountable for his father's sin despite his advising him?

Maintaining kinship ties (Silat al-Rahim) is not restricted to visiting; rather, it encompasses everything that is considered a connection according to custom. It can be achieved through financial support, fulfilling needs, visiting, writing letters, exchanging greetings via messages, and similar acts. The kinship ties that are obligatory to maintain are with relatives between whom there is a prohibitory degree of relationship (mahramiyyah).

No one bears the sin of another, and illness and afflictions are not necessarily punishments; rather, they may be a sign of Allah's love and a means of elevating one's status and attaining reward.