Legal Advice Needed: Rent to own agreement, owner died, no next of kin. Options?

I need advice for a client whose adult son has been renting to own a property in Los Angeles County, California. The arrangement was informal, with rent paid in cash or credited for property work. The landlord passed away 2+ years ago and there doesn't seem to be any next of kin. The son has been maintaining the property without paying rent (because there is nobody to pay). At this point, property taxes are adding up and major repairs are needed. The son wants to know: Can he obtain ownership of the property through a quiet title action, adverse possession, or another instrument? If yes, what's the process and what are the chances of success? If not, can he get reimbursed for property taxes and repairs he has made and how can he recover the portion of his rent payments that were set aside pursuant to his "rent to own" agreement. In either event, As long as he pays property taxes and maintains the property, can he continue living there rent-free until someone with rights to the property appears or it escheats to the state? Lastly, if he isn't able to obtain an ownership interest, what do you expect to happen with the property and what is the timeline in that situation? If this isn't your expertise, any information or referrals would be greatly appreciated. If you can assist and see a viable path forward, I'll connect you and the principal directly. Thank you very much for your time and consideration.