Legal Question in Criminal Law in California

More than one person can possess the same item at the same time - it's called "joint possession." Essentially, if your husband had access to the weapon and knowledge that it was there, he can be convicted of possessing it.

Can he get his own trial? His attorney would have to show some sort of legal, compelling reason to grant a separate trial. Ordinarily, the preference is to keep people together so they don't end up doing 4 trials when the evidence is essentially the same for each one. Your husband's attorney is in the best position to assess whether there are grounds to try and ask to sever your husband's case from the other defendants.