Legal Question in Real Estate Law in California

You have not said how the title is held. "Split" is not a legal term of title. Most forms of shared title, however, carry with them an undivided right to occupancy of the property. So the other sibling is probably powerless to stop you; they are not even entitled to rent. On the other hand, however, when joint owners of property cannot agree on its use and management, either one can force a sale of the propoerty and distribution of the proceeds, in an action for partition. So if push comes to shove, they can keep you from occupying the property that way.

The previous answer is accurate, to a point. If the siblings are co-owners as tenants in common (more likely) or as joint tenants, each has a right to possession of the entire property, concurrent with the other's identical right. The co-owners are, in a sense, involuntary housemates. There is indeed also a remedy for unhappy co-owners, a lawsuit for "partition."

However, two other concepts are worthy of mention. If co-owner X becomes a "cotenant in possession" by moving in first after the renters are gone, X has a somewhat superior position, despite the theoretical concurrent right of possession of co-owner Y. This is because the law frowns on anyone asserting their right of possession by self-help, without legal process; this is, for example, why we have formalized eviction procedures. Y cannot simply force the locks and slip in while X is at the movies. This principle is somewhat in X's favor.

The other concept is that Y has a remedy if X gets into sole possession and Y desires to exercise his right. The exclusion of Y by X, against Y's will, is called at "ouster." The law contains a couple of provisions for Y to regain shared possession, or obtain damages for the ouster. See Civil Code section 843 for introductory procedures to establish an ouster and begin the process to recover co-possession or damages.