The Seven Oaks are actually names associated with the seven heroes from the founding, and now the seven ruling kingdoms.

Black Oak
Red Oak
White Oak
Pin Oak
Bur Oak
Sawtooth Oak
Water Oak

Twice a year, on the solstice, there is a conclave of the Kings, they meet at the Hallowed Grove, where the seven trees grow, and there the kings will make laws.  Here they will also receive the new Judges from the Druids who were picked the year before.  At this time the Druids and Priests pick new judges to be trained from the commoners who arrive there, no noble may ever be a judge.  The judge will then spend a year with the druids and priests, learning and being trained to receive the gift of Discernment, a special ability to see through lies.  When they pass through the final rites they will be given to the kingdoms to enforce the laws given by the Kings on King and Commoner alike.