Perhaps you should consider hiring a local attorney that specializes in landlord/tenant law & evictions.
http://www.legalwiz.com/morearticles/California_Landlord's_Guide_to_the_Eviction_Process/?objectID=328
WHAT IS AN ARRIETTA CLAIM?
Sometimes when the Sheriff attempts to perform the final lockout, a third party will hand a Claim of Right to Possession form to the Sheriff in which that individual claims to have been an occupant of the property but was not named in the unlawful detainer complaint. The Sheriff will have to immediately stop the lockout until the court hears the occupant's allegations at a hearing within a week or if the occupant posts 15 days rent, the hearing will take place anywhere from one to two weeks later.
If the Court decides that the claim is valid, the Landlord must start the whole eviction process over again as to that tenant by serving a new notice followed by the summons and complaint which the occupant can contest by filing any one of the above responses. If the claim is denied, the court will order the Sheriff to continue with the lockout.
Important: The only way to prevent an Arrieta claim is to either serve everyone in possession or to serve a form with the summons and complaint known as a Pre-judgment Claim of Right to Possession. This form gives any unnamed occupant the right to identify himself or herself so that the Landlord can proceed against them. The drawback of filing this form is that it delays the case by an additional five days since the unknown occupant has ten days to respond instead of only five. If you suspect that your original tenants have allowed numerous sub-tenants to move into the rental unit, it is strongly advised that the Pre-judgment Claim form be filed and served. It is the policy of our office to serve a Pre-Judgment Claim in all cases unless we are advised by the Landlord that they do not want it served because there are no unauthorized occupants in the premises