Legal Question in Landlord & Tenant Law in California

Well, yes and no. Joint legal ownership or possession of real property creates an odd legal situation in which each owner or possessor (such as a tenant) has all the rights and responsibilities as if they were the only owner or occupant. So you have the right to throw the person out, and the other tenant has the right to invite them right back in again.x I suppose, in theory, you could initiate a partition action of the leasehold, as if were joint owners, but that would cost thousands of dollars just to get filed. So the bottom line is that you don't have a law-based answer to this problem. You're going to have to work something out or move out.