WHOA! chill friend, I never said that I would do it (I'd certainly allow it as a DM)
If the Wizard went out of his way to gather 4 other spellcasters with Tattoo focus, then you bet your ass I'd allow this Besides, In my games, I ALWAYS make people regret every single exploited action they make "Oh you want to make an army of Ice Assassin using Circle magic? Alright then the other participants gain as much control over the Ice Assassins as you do."