Now everyone. I know the author isn't planing that far, butt.... We only see them on MC radar and interfering with the story the strongest, while they are in his town. And if he had killed them while they are there, other nobles would have investigated their deaths or would have judge him guilty from the beginning (which would have been true) OR would have judged, that the security of the city is shit and that MC is unfit to rule over ityaddayaddayadda. Welp,...the point is: other nobles and even more bloodshed in their wake. And look at those clowns: They are like Team Rocket. Jessie and James never hired killers! Who would have guessed they really posed actually that much danger? More than another noble? Or a banana.
Now, would they have been killed somewhere else, I mean in their home or while traveling (, but not on the way to or back from that city), now that might have worked. Then again their deaths would have alerted, whom? Right, more nobles. And they would have looked into his former domain.
I'm surprised though MC goes for the girl even though he didn't made any too obvious moves before. That's refreshingly realistic.