Other option would be to sell one of these homes and buy a single family home on a larger, flatter lot with more potential to build, but then I lose these great mortgages I've got.  

You magically get the seller to cover every single closing cost (A $12k gift, or a trick to get you to buy their problem.).

You will typically need be at $500k+ purchase points but its usually worth it vs buying lower class areas or single families.

They knew all along this was an LLC, every single paperwork sent to them was under the LLC. 

Every flipper has found themselves at Lowe's for the fourth time in a single day, picking up yet another piece of material for a project.

I do single family "off market" that I take over with owner financing, subject to, wraps and lease options.

Buying a single-family home with a detached garage and converting it to an ADU is much simpler.

The ADU is a good idea for property maximization, but unless it has a separate driveway, it will push your rent in the main house down some because then you aren't renting a single-family house on a lot by itself.

I am going to be lending to an investor on a single family home. 

I do expect greater development of condos and townhomes and higher density single family communities. - Acreage will continue to be a very hot commodity.