It is very tough to follow your story. I think you said meth was found underneath the hood of the vehicle that belonged to the driver. No one owned up to the meth. If the meth was found underneath the hood, the other passengers should have a good case for a dismissal. The law states that possession is what is within the reach of an individual. This would not be within the passenger's reach.
Seth Weinstein, Esq.
Practicing throughout Southern California
This reply should NOT be considered a legal opinion of your case / inquiry. At this time I do not have sufficient factual/legal documentation to give a complete answer to your question and there may be more to the issues you raised then I have set out in my brief reply.
Passengers are generally not criminally liable for contraband found in a vehicle unless it was under their seat or within their reach. The driver is responsible for contraband in the vehicle.
I'm curious why they got stopped and how the reason for the stop justified looking under the hood. (I'm not asking you to answer this; I'm just musing on the 4th Amendment issue.)
In a trial for allegedly violating Health and Safety Code section 11377 (possession of meth) the DA must establish, among other things, that the accused actually knew of the presence of the meth. From your description in your question, your boyfriend did not know it was there.
Please stop talking about this, though. Your boyfriend needs to keep quiet, too. When people are facing criminal charges and the prospect of going to jail, friendships tend to slip by the wayside. It's just better to be discreet and not generate any rumors or gossip.