The main downside is the loan limits for a house with ADU match a single family, not those of a duplex (which is higher).Rent control applies to MF where unit is older than 15 years old.  

I got my license within the year and I'm having difficulties adopting my brokerages daily routines and general systems.

There are many things we can't control even if we did our best due diligence.

It started snowballing out of control and that was if the ADU was permittable in the first place.

We decided to diversify in a few ways...given as a Broker Owner we only controlled TWO things, our roster and more effectively monetization of ALL our transactions.  

You'll have to put a tad more money into the deal or have them control 100% of the renovation, but don't let that stop you from reaching out to get financing.

If each building belonged to a different owner, the only thing that they would have to collaborate on is, obviously, the courtyard (gardening, each side has it's own sprinkler system) , the intercom (about $120/month for the phone line), and the parking area (needs resurfacing).  

Systems and SOPs are KEY!

Interested to see others experience as I know price ranges and rehab budgets control quite a bit of this.

Banking on a hope that "if" something that you can't control happens, you "might" start to get positive CF starting in a few more years (also losing money) so you might recover all of your losses in about 10 years, is ridiculous.