Legal Question in Landlord & Tenant Law in California

The three day notice is personally served upon the tenants; there is no proof of service required. Once they fail to comply within the "three day" period, then you have to serve them [using a non-party to do the service] with the unlawful detainer lawsuit. I am unsure what you did. If you merely sent them a certified letter with the 3 day notice enclosed, that is not proper service. You must make several reasonable attempts to serve them in person [each defendant must be served personally and not just one, and you need to serve individually everyone living in the unit, except for minor children, even if they are not on the lease]. If that proves unsuccessful, then you can try substituted service [giving it personally to person reasonably anticipated to give it to them] and if theat does not work, you post the notice on the outside of the unit in an obvious place and mail a copy to all residents in the unit. after the three days has run [first day not counted], you then have to serve everyone with the lawsuit. If you do not correctly follow all the requirements, your case will likely be dismissed