Legal Question in Real Estate Law in California

The county can't "legalize the deal." The county doesn't "allow you to take over" property. The county only maintains records of documents submitted for recording. That doesn't make the documents legal or not legal, valid or not valid, or enforceable or unenforceable. A deed from a legal owner, to the owner and you jointly, makes you a partial owner. If you don't have one, you're not a partial owner. And unless the lender agrees to allow you to assume the loan, the assumption agreement is meaningless and recording it makes no difference.