Cane's mother, Crystal, was born to the late queen, while Aeon was born to the first concubine. By the time his mother was born, Aeon had already been appointed as the Crown Prince and by the time the power struggle for the throne started, Crystal had been mated to Josh, the Alpha of the Howling Wolf pack.
In order not to be dragged into that bloody battle, Crystal firmed her status as the Luna of the Howling Wolf pack and expressed she had no interest in the throne. She had never wanted it in the first place after all.
Therefore, Crystal, Randy and Osana, Aeon's little sister, were the only children from the late King that managed to survive during the power battle in the palace.
Supposedly, if Cane's mother wanted to take the throne, she had every right to get it, because she was the legitimate princess, the only child that was born from the Queen.