Legal Question in Landlord & Tenant Law in California

If they do not have a legal right to be there, yes. If they have a signed lease, whether month to month or for a fixed term, say a year, then you will need a reason to evict, say they are not paying the agreed upon rent.

If they mere are a guest, they are no different than someone who comes over to your home for a dinner party and then will not leave on their own. you show them the door and say leave.

If you ever accepted rent from them they have the rights of a tenant or boarder, depending on the details of the situation and any agreement that might exist. If they have never paid rent, however, then the previous answers are correct.