What is the position of Islamic law on a man over eighty years old who claims to know the unseen and divine revelation and to speak with the Creator, and who causes family problems due to these claims?

Claiming knowledge of the unseen and direct communication with Allah is clear disbelief that expels its claimant from the fold of Islam, unless they are mentally incapacitated, because knowledge of the unseen belongs to Allah alone. Whoever goes to a soothsayer and believes him has disbelieved. This man's lies must be unequivocally rejected, and there should be a call to truth and an clarification of his matter to the people.