This appears to be a situation that falls under something called the "Doctrine of Constructive Possession." This doctrine extends possession to individuals who didn't have hands-on possession of something illegal. I may be wrong, but I think in most cases, courts say constructive possession exists when a person merely has knowledge of an illegal object and, at any point, the ability to control it.
I am by no means a lawyer. I would assume the courts think you did, in fact, have knowledge the meth was in your house and, therefore, the ability to do something about it before you left for two weeks. Because no one in the house took responsibility for it, everyone is viewed as guilty. I would think it would be wise to contact a good lawyer in your area with knowledge of California's possession laws.
I hope this link helps explain things a little better until you speak with an attorney. Good luck with your situation.
(removed)