After researching quite a bit, I decided that finding architects and a modular build consultancy and arranging the GC myself is probably the way to go.

You get grandfathered into the codes that were in place at the time, you get the old setbacks, you don't pay an architect, engineer, city and permit fees, plan check costs, school fees and other costs that will not come with an existing house.Not saying that you can't build new for less than a remodel, but not usually when you add in all the costs above. 

@Jingru Sui Hello I live in powder springs and I’m in architect.

That technically triggered the requirement to get a COO before they moved back in.... but no one paid much attention to this, not myself, not the architect, not the customer, and not even the officials at the little high-end SoCal beach city.

Project architect/designer, commercial and multifamily investorYes there are many things wrong with California.

I talked to two prominent local real estate brokers who told me they are sitting on numerous listings that are "on hold" because of this pandemic. 

I also never use that phrase myself and am very skeptical when I hear it from other contractors.I seem to be stuck more with the issue of him having to contribute and do more so his partners can gain....He has to use his contactsSchedule estimates with subsMeet with subsDraw up scope of work Draw up contractsMeet with townMeet w architect Draw up contractsLook at plansUse his insuranceHis crew for laborWorkmans comp.Collect paymentsfile taxes etcThe list goes on and on and I feel there needs to be compensation for all of that.Which brings up the question, assuming all partners were financially invested equally what else did his partners bring to this deal that they have to provide extra time and effort and personal resources for no gain?

There are other differences also, so you would need a decent architect and/or engineer on board.Financing should be the same as a duplex, at least that is what I have been told by my bank.  

If not, the city does not have to honor the 2 family use and could require a new use permit where you would need to have an architect or civil engineer submit a new zoning plan and obtain a zoning permit. 

That said,  now that we have been in 'housing crisis' mode for a few more years,  and more construction and architect types are available due to economic slowdown,   it might be worth revisiting.