Rights as a landlord

[Omar Catalan]

Hi all, I am in California. I have tenant under a 1 yr agreement that terminates at the end of October. She moved in her sons father about 6 months ago and they are now having relationship problems and refuses to move out. He is not on the lease agreement and she is not willing to add him to the contract. What legal rights do I have to remove him from the property. What action should I take from here?