There are twelve signs of the Zodiac? Ummmm...
Including seven sisters who are all trying to kill each other, there are
twelve main characters in my idea for the second book in the series I have planned out in my head

. Those seven sisters, their main assistant in the business they jointly run, the two protagonists, a guy teaching the male protagonist basic magic, and the former boss of the female protagonist.
7 + 1 + 2 + 1 + 1 = 12
HAH!