My biggest issue is with the youngest ones breaking the 8th commandment and bearing false witness. They try to frame their siblings for something to get back them. But I have slowed that down a lot by never believing a report of theirs (even though secretly I'll investigate and can usually outwit them and get to the truth of it) to deter unsubstantiated allegations. I cross-examine both their versions of the story until one slips up and contradicts himself (which they eventually will do if they're lying). One time, and this was an easy one, a younger sibling wrote the older sibling's name on the wall in crayon ... to get him in trouble. But her handwriting gave her away. She made her "i" with a big circle on top so that it looked like a lollipop. When two kids are fighting and both are blaming the other party for having "started it", I usually punish them both. I told them that because both have been dishonest in the past, I can't believe either one, so both get in trouble (since fighting usually requires two to participate). So that actually has inspired them to be more truthful over time in order to establish their credibility.