Remember I'm intending to limit it to a single +12 bonus to the leader, not everybody.
I get that your argument is that it opens the door for other powers which are less restrictive and more abusive.Now I'm asking what you would replace the portion of the power with that fills the same thematic roll of "working with the family = stronger rituals".
That is true, but I wouldn't want to go lower than -3 so it still costs at least -1 refresh for the full on sorcerer or wizard family member.