The Kozuki were one of the clans in charge of Wano Kuni and they still let this witch hunt go completely unpunished. Whether they had a hand or not in actually killing the innocent members of the Kurozumi clan, they're absolutely responsible for letting these vigilantes of justice do as they please
Bruh even Oden himself says that his own clan hid some shit behind the curtains
Oden could admit it because he wasn't shady lmao. He would've let the whole shit go.
Which was all before Sukiyaki. With the initial thefts Orochi was already going to be rich and with Oden (Hyo and Yasuie as well) around, Orochi and Kanjuro were protected from any threats. He even had the chance to be a decent shogun, the rebellions happened because he trashed Wano. Kaido wouldn't have been able to win without him and wouldn't have been necessary as an ally anyway. Instead he lost sleep for twenty years to paranoia and got betrayed by Kaido, while Kanjuro suffered alongside the Scabbards and is being finished here.
Even if there was a point for them to make by sparing Orochi, the Kurozumi clan has already proven that they'll keep seeking revenge beyond whatever is offered.