Q: Can a prenup grant ownership of property not solely owned by one spouse?

A: I think the bigger issue here and the real problem is that your prenup does not sufficiently identify this property. You say that the prenup does not specify the property's address. The property is also described in your prenup as a "jointly owned" property when in fact that also is not accurate. I'm thinking that that clause/that part of your prenup may be invalid and not enforceable. The property in question will need to be dealt with in your divorce. Given that this property appears to have been your separate property prior to marriage, your soon-to-be ex may be entitled to an interest in this property, only to the extent that the community made mortgage payments on this property during the marriage (I'm only assuming). If the community made mortgage payments on this property during the marriage, the community acquired a certain interest in this property to which your soon-to-be ex would be entitled to one-half of that interest, whatever it is. Furthermore, if your previous spouse is still on title, you may need to file a partition action if some other type of agreement cannot be reached by the 3 parties involved.

A: You cannot give Sam 50% title to a house that you and John own just by naming a “rental property” in a premarital agreement. That contract allocates rights between you and Sam; it does not bind John or alter the deed.

California law requires a signed deed from the titled owners to transfer an interest in real property. Because only you and John hold title and no deed added Sam, the prenup did not convey ownership and the record remains exactly as it reads.

At most, the prenup could create a contractual promise between you and Sam about how to treat your own share—such as splitting income or proceeds—or it might support a reimbursement claim. It cannot divest John of his interest or make Sam a co‑owner against the world.

The undefined reference to a “rental property” also undermines enforceability under the Statute of Frauds; courts expect a property description specific enough to identify the parcel. Your plan to refinance never closed, so the contemplated transfer never occurred.

Bottom line: Sam can seek contractual remedies against you if the agreement supports them, but he does not hold a 50% ownership interest in the home itself without a deed executed by the owners.