Before probate closes, an heir/beneficiary doesn't own specific real property they hold an expectant, contingent interest in the estate (a right to eventual distribution). You can't get a deed to the house itself yet. What you can acquire is an assignment of the heir's beneficial interest basically, you step into their shoes as the person entitled to whatever they would have received when the estate is distributed. This is done through a private purchase/assignment agreement, sometimes coupled with a "notice of assignment" filed with the probate court so the personal representative and court know to distribute to you (or your entity) instead of the heir.
The governing statute: Cal. Probate Code § 11604.5
This is the key law you need to know cold. It applies specifically when a transferee acquires a beneficiary's interest "for value" (cash or other consideration) and it applies with extra scrutiny if you, as the buyer, regularly engage in purchasing beneficial interests in estates for consideration