Buying a property, existing rent agreement cant be provided to me

[Alex Parish]

Hey everyone, I am buying my first 4-plex property in rent controlled Los Angeles. This is a probate sale with every strange twist you can imagine, however I have gotten to the point where my offer is in lead position and is likely to be accepted. One of the issues regarding this probate sale is that no one, including the executor of the estate, has access to any rental agreements or past payment history prior to the estate taking over except possibly for the estranged ex husband that refuses to cooperate. The rent being paid to the estate currently is essentially what the tenants claim they were paying prior to the home owner's death, but they all seem to be paying in cash and paying an amount way under value for the area. These re the rents I stand to receive once I take ownership. 

Is there any way I can determine the actual rent these tenants were paying prior to the original owners death? If there are no lease agreements being provided to me, does an agreement exist after I take ownership or are these tenants considered month to month? The tenants can sign an estoppel, but that only acts as a support to an existing agreement, correct? Do I have any right to evict these tenants if no lease documents can be provided to me, and if so am I responsible for the relocation fees? It also seems no one has paid Rent Stabilization Fees or kept the rental registration up for the city. 

I do not want to remove them, but the investment does not make much sense at the rate they are claiming to be paying. Any help is much appreciated!