Whether you decide to buy from the LLC sub-to, or pay cash, go through a title company to make sure the seller can legally convey title to you. Then you're covered if anything comes up later.
Does the seller have a POA or loan authorization form for the existing mortgage signed by the original owner/s? If so it shouldn't be too difficult to reinstate the loan and/or pay it off.
Excess proceeds go to the equitable title holder at the time of sale. Not exactly sure how it works in CA, but here in Arizona the party entitled to those funds has to prove they were the property owner.
Letting the house go to auction is the worst possible outcome for the original owner, huge hit to their credit score and the foreclosure sticks with them for a long time. When you reinstate their loan and start making payments again their credit gets repaired very quickly. I've done sub-to deals with homeowners in foreclosure where I reinstated, made 3-4 payments and the owner's score increased by over 75 points.