Legal Question in Landlord & Tenant Law in California

A rental agreement can be verbal and fully valid, for up to a year. You definitely need to give them 24 hours notice to inspect if they live there and pay rent, regardless of anything else. As far as getting back in the property, you have a real mess. Even if you terminate the lease, the ex can reinstate it. Co-owners of property (unless it is one of several arcane and very rare forms of joint ownership) have full rights of ownership as if they each owned it separately. So really neither of you can do anything without the cooperation of the other, except that when rights are granted by either of you to third parties, you run the risk of wrongful interference with those rights. The only solution when co-owners cannot cooperate, is a partition action in court. Historically that resulted in actual division of a piece of property. In modern times, particularly with modern subdivision laws, partition by sale is the method the courts use, and it is in many ways like a partnership dissolution. That is true in both the principals applied, and in the fact that it very quickly can become so expensive in legal fees that the parties either start cooperating or work out the dissolution themselves with a market sale of the property. So you and the ex need to work this out, or one of you has to file a partition action to show the other they are serious, and then work it out. These are REALLY good situations to jointly get the help of a mediator.