Legal Question in Real Estate Law in California

I would recommend two basic actions, with some sub-recommendations.

First, the basic actions are to be in touch with the subtenants to make sure they understand that any hostility you show toward the tenant is not intended toward them; and, to pursue the eviction promptly and according to law.

The sub-recommendations complicate the picture at least a bit. One problem is that the tenant is the one who is in contract with the subtenant, and if you deal directly with the subtenant except perhaps to reassure them that you don't dislike them too, you could be accused of "interference with prospective economic advantage" which can be a tort. A somewhat remote possibilityn is advised. The next sub-recommendation is that you need to follow up on your three-day notice (if rent isn't paid) by filing and serving a lawsuit for unlawful detainer.

If you are not an experienced landlord, I'd recommend either getting an attorney or using a self-help law book, usually a paperback, on basic landlording skills. Be sure it is based on California's law, and Nolo Press is one highly-regarded publisher.

Finally, if the tenant has given possession to the subtenants, be sure that any papers you serve on the tenant are actually delivered to him/her wherever he/she is to be found, and not merely left at the property or delivered to the subtenants.