Another idea I have is buying a SFR with a legal attached apartment and live in the apartment while renting out the majority of the house seeing I don’t need much room.

You should assume you will need to pay off the first, including any back payments, late fees, and legal fees. 

We find the best structure is to form a legal partnership.

The best way to avoid this is to make sure you have that property under contract and everything written on paper/legal documents.

I strongly suggest you ask either a licensed local hard money lender or licensed CA real estate broker to legally originate your loan for you.

If you are changing the legal addresses of the units, you better check with your municipality as to what is involved.

I am looking into the legality of having them all sign new leases now, or possibly adding addendum.

If the law requires 60 day notice in your case, it is generally is from the date of the legal notice. 

By creating the LLC, you are insulating yourself personally, should you experience any legal complications.

Not sure how long legally you'd have to stay in the unit, but I imagine it's too long to make it worth it because I've never heard of anyone doing that just to get rid of a rent-controlled tenant.You can Ellis the entire property, meaning you take all units of the property off the rental market for a certain period of time.