Maybe there is a limit, they all just have different tactics, kind of like the Nightfalls etc...
1, 2, and 3 were priests. Maybe 4, 5, and 6 are infiltrators. That might mean that 7, 8, and 9 are heroes or something. If we execute too many sons we could be overwhelmed with Daimon armies if we don't get rid of the Nightfalls...