Controlling all of Lai Yin's heirs and then killing them at the right opportunity was originally part of Blood Queen's plan.
But her plan couldn't be so simple and crude; it must be like causing the death of the City Lord, either by poisoning or by creating various accidents, definitely not like now, with several heirs being assassinated at the same time;
Although Suravi sensed something wrong, he sent the City Lord Mansion guards to the side of each heir with inheritance rights, claiming it was for protection, but in reality, it was surveillance.
Once City Lord Lai Yin died, Blood Queen controlling the entire city as the City Lord's wife would not be very reasonable. The best approach would be to support an heir, make them the City Lord, and gradually insert her own confidants. Once all the rights in the City of Sin were in her hands, it would no longer matter whether there was a City Lord.