Take care of the bedbugs (see CCS 1941 below) within 30 days and you should be fine. I agree with ucodegen and would recommend moving the tenants out. End of story.
What happens if you don’t? Lets say they already provided you a letter in writing letting you know that they have bed bugs. They can just take pictures of the infestation and provide a letter letting you know that they are vacating (using CCS 1942) and request a final walk through. You’ll receive a prorated rent check through the last day with the memo portion saying “Civil Code 1942 termination prorated”. If you go to court, it will cost you more, and you still have to take care of the bed bugs.
Civil Code Section 1941.1 paragraph 1, Health and Safety Code Sections 17920.3, 17920.10.
A rental unit may be considered uninhabitable (unlivable) if it … is a substandard building because [of] … inadequate sanitation, or a nuisance endangers the health, life, safety, property, or welfare of the occupants or the public.”
