Legal Question in Real Estate Law in California

The right thing to do is dependent upon whether you lived in the same house at the time you rented the two rooms -- in which case the people living there originally were "lodgers" rather than true tenants. If the original renters had exclusive use of the house and you didn't live there, they would be classified as tenants.

The difference is important. Lodgers are there in the house on a mere license, which is revocable at any time, and personal, so it cannot be assigned. When you tell a lodger to leave, they become trespassers after a reasonable opportunity to pack up and go, and their removal after that should be a police matter, not a civil matter, but do note that the cops are busy and don't need extra work and are inclined to say everything is a "civil matter" if they have any doubt -- and they aren't lawyers.

On the other hand, tenants have much stronger rights, including the right to longer notice and a formal eviction procedure. You should get a couple of those paperback books on tenants' rights and how to be a landlord and read up. Doing and selling drugs is a sufficient ground for a landlord to evict a tenant.

As to personal threats, break-ins and so forth, I think this is cause for alarm, and you should check with your court to see if they have a domestic violence advisor who can assist you in getting a restraining order if the occupant is only a lodger and thus is subject to immediate removal. I would not tolerate this stuff another day without getting local advice and shelter if warranted.

If he has never legally been living there, and he does not have keys, he is guilty of a crime. Call the police.