Experience matters. A track record of successful conversions beyond researching.   Do you have it?  I wouldn't be attempting any such action without experienced representation.  

I would have to seek the advice of a local real estate attorney, Maeve. That is not in my wheelhouse OR my state!

Good luck!

I have no experience with conversions and I suspect you will need to involve some serious legal help in the process.

Maeve,

I admire your ingenuity.  I would definitely seek the advice of a real estate attorney as to how this could be done. Depending on which part of Los Angeles you are talking about, there  may be building issues, permits, etc.  You would need to consult a builder who has done this type of conversion.  The costs may be prohibitive as well as the time that is needed to do this.  At some point, you may have to hire an expeditor to ease your client's pain through the bureaucratic highway.  Frankly, having worked on the commercial real estate side of  Los Angeles, I think that you may be taking the long hard road with no guaranteed results. having spent many dollars A.

Interesting question here but not in my area of expertise 

I agree, selling is generally better than renting for most people.

Check with a few investors in this municipality who have done these conversions as well as a few good real estate attnys.

I have never done this Maeve Becker but I would consult an attorney.  Does his sister want to buy his share? Where in Texas is your client moving to?  I'm in greater Dallas Fort Worth and would love to help your client if he's planning to move to the area. 

GREAT question Maeve Becker . Totally out of my area of expertise but I'm eager to read the solutions presented by others.

You probably should see a CA real estate attorney.

Real estate attorney time!

Besides getting an attorney involved, someone would have to go to zoning to see if it is feasible.

 Maeve:

CONDO CONVERSION

You have several options, though I suspect a condo conversion will be the least attractive among them.  It’s a very expensive process and usually justified in situations in which investment optimization is the goal. The process follows the California Subdivision Map Act and brings a litany of fees involving attorneys (conversion and hoa docs), application fees, surveyors, deconstruction contractors, inspectors, among others. For a two family duplex, it’s difficult to imagine getting past a cost-benefit analysis.

 RE-FI

 As a Realtor, I’m sure you’ve had this discussion with your client, so I’ll forgo comments in this regard.

PARTITION

I have the impression this is a simple disagreement between siblings. Court intervention is probably an extreme solution.  For your edification, an action to Partition by Sale may occur between feuding family members with a common property interest. After the case is filed, a request for an interlocutory judgment is requested. This is fancy term for temporary or provisional judgment (before final judgment) to ascertain the party’s respective interests.

But you don’t necessarily need court intervention.  You can also partition by appraisal, which is terminology close to speaking for itself.

 OTHER OPTIONS

 The options, above, aren’t exhaustive, but I'd need more facts.

LEGAL ADVICE DISCLAIMER 

I present these options as a full time California real estate attorney and broker of 30 years.  If your client genuinely needs a specific solution, by all means, reach out. For the moment, this discussion is for educational purposes only.  Neither you nor your client should rely on these comments in lieu of retained counsel.

The coversion is a good plan but you are going to have to get good local  help. Find out who in your area is putting together condominium declarations & public offering statements and find out how much that is going to cost - all the legal stuff. Then contact the city/county and find what if any physical changes may be required to the building and get bids for those. Building & codes is different in our area for a condo vs a duplex and upgrades to buildings are usually required to condominiumize a MF building.  Then with those costs and time lines known, decide if you still want to do the conversion or simply sell the 50% ownership to the sister and work out how the financing for that will work if the sister doesn't have the money.

Another possible option is to see if the duplex can be converted into two "zero lot line" homes rather than coverting to condos.

If they have separate legald escriptions this shouldn't be an issue. At least in Oklahoma it is not difficult to get the legal changed from 1 to 2 and have half duplexes.

Do they share the same APR? I had a similar situation in Malibu. I called county assessor and learned about the process. It would take about 2 months to separate units in duplex. Both homeowners agreed at first to share the cost( it was not an outrages cost for the process: the appraiser+ county+ city fees+ title changes fee.... I do not remember details since i simply connected them to the rep). However, the homeowners could not wait and do it themselves,  due the health issues, they sold the unit as is, giving a credit for this to a future buyer who paid cash ( financing and title in such situations  of selling a clouded deed would be an issue)

Go to zoning and ask questions. That’s where I’d start, then contact other professionals in your area to gain insight. Good luck to you

1. Sell to his sister 

OR

2. California Partition Action 

Not here but did have experience back in Boston. First step is probably a good real estate attorney familiar with what has to be done legally to create the 2 condos, file the paperwork, create the condo documents, etc.

Different rules and regulations in different places.... I did many of them in the 1980's.... everything was loosey goosey then, and I took advantage of it.... I needed an land engineer to survey the property; draw the floor plans of each unit; and then an attorney to produce condo docs plus rules and regulations.... 

 This was an easy task back then... I did a duplex; one four family home; and two six unit buildings.... did not put any work into them.... as is.... presold before I closed on each building....

In IL a duplex owns the land. Resubdivide & make 2 seperate units. Sis can live there forever then with new neighbors.

See if the property qualifies for such a thing. Then, also check the zoning as it may be eligible for multiple units. This all leads to recognizing the highest and best use (and $$$ values) of the property. Also consider selling it as a life estate where the sister gets to stay there until...?  Then, rent out the other unit. To certain investors, this is a good place to park funds and buy time too

Michael Jacobs covered it.

Seek advice from your attorney.

I'd go first to my broker

and then to a qualified CA RE Attorney to review the deed, any restrictions (FRIR for the sister? Any other owners or is it 50-50?)

CPA to investigate possible tax implications (property's been owned 70 years--Prop 13 taxes? Would that change?)
(I've been out of LA since the 92 riots so IDK what has changed or would in event of a conversion)

and to City to research feasibility per the General Plan, zoning restrictions etc.

Gotta love family dynamics. :D

Consult a good real estate attorney with experience in condo conversions and document writing experience.

Here in NH a real estate attorney prepares the condo docs and proposed deeds. They have to submit to the NH AG's office for approval. It could take 30-45 days.

Sorry, no experience with conversions here.  I do hear that they are popular though in rent controlled areas.

Conversion from R2 to 2R1q(attached) is more lucrative.

A lot of Beach Communities do this all the time

That sounds like a great project, good luck.

I don't know, will read answers.

Time and money in CA. if it is anything like here in WA.

Have to see what otheres have to say!