The wrong or right
Out of all the leaders that Leo and his group could have selected to try and interrogate, it appeared as if their luck had made them choose the very same one that Arthur had decided to go for. Seeing him appear, confirmed their thoughts that the twelfth family had been on the original Punisher's hit list.
Leo had managed to figure out something else as well. The low amount of forces in the twelfth castle... it was done on purpose.
The number was just perfect to make the intruders seem like a menace, but not to the point that the leader had to come out and deal with them. As such, Kim Prima was still in the throne room, which was exactly where Arthur had wanted her to be.