Is it possible for someone to know the time of death of the sister or her child through "her chart" with which she was born in the month of Ramadan, and is this matter considered part of the knowledge of the unseen which only God knows?

No one can know the time of death of a child or their mother, as this is part of the knowledge of the unseen that Allah has kept exclusively for Himself. No attention should be paid to such claims, for there is no authentic text proving a connection between the falling of a leaf and the death of a person. Even if such a connection were proven, it is impossible for this claimant to have knowledge of the unseen.