I suggest that the monster level up at their lairs be applied to each of the monsters. I wouldn't mind it if the creature lair had the party leader gain levels faster than the others in the group. I suggest this because if I attack these layers later in the game I destroy the other back-ups for the brute and then it becomes a easy battle between 1 creature with big hit-points. It would provide a better challenge if the other monsters gained some levels and make clearing these monster lairs more important early on.
