??? Why would they kill the moms?
I don't know some of them like Tserriednich don't really care about other human life at all, Benjamin is ruthless and opportunistic.
With her only son Sale Sale gone, Swinko Swinko probably has to ally with another Prince, probably someone that would punish the murderer. That is, if Togashi didn't forget about it completely as he aprubtly jumped to other plot points.
Realistically, I think he should kill them because there's too many characters and I don't want to wait another decace or whatever I've waited here for it to continue. If a Prince dies, the staff affiliated with them drops out of service, except for the guards affiliated with the mom which would only drop out if the mom dies. Anyways since he has only even halfway started with the mafia stuff, I'd expect character count to only further increase in this run, so I think there has to be slaughter to compensate.