If I were a lawyer and I had a moth roach pet that was a ghost role I would absolutely prosecute you for murdering my sentient moth roach.
And I think I could probably win if I had witnesses of the mothroach being smart/ doing flips/ whatever.
Either way though, the fact that the ghost role vermins CAN become sentient, regardless of your personal threshhold for when you think that status is acquired, means they CANNOT be KOS.