Legal Question in Personal Injury in California

By definition, negligent actions are unintentional. But aiding and abetting are intentional actions -- and they're part of criminal law, not civil. So even if the people you describe were all in California, I don't see how A could be liable for B's negligence.

If B's actions were intentional then A might be liable, but not as an aider or abettor. Whether other states or countries could hold him liable will depend on their laws.

You are mixing up different legal doctrines in a way that is nonsensical. Aiding and abetting are criminal terms, and they apply to intentional acts as pointed out by Mr. Hoffman. Negligence is a failure to use care that causes harm to others and is a civil tort doctrine.