These houses are fairly big size within an in-law portion with in the house (not an ADU). if we rent out the in-law portion separately, would there be privacy concerns for the main house renters?

They're only  used for privacy walls and decorative pieces, not for structural/building materials but still, nice to see waste being upcycled for different uses. 

His method is not for me as I will be house hacking with my fiancé, and we look forward to our privacy.

It ultimately comes down to your budget and desired level of privacy in your living situation.

However, privacy concerns triumph and the fact that you have multiple independent parties sharing rented space does not mean the tenants have relinquished their privacy rights. 

Other than shared walls, a side-by-side plex offers the feeling of a townhome or apartment where there's a fair amount of privacy (great for families or couples).

or are Real Estate agents sworn to some clients privacy information?

Time to roll our TN cabin into something bigger. We’re looking to upsize it and a couple of LTR’s into one property and use the equity for something on Long Island, NY. This has been our exit plan to transition to few...

Generally speaking, most states will not allow any sort of camera to be mounted facing an area where the tenant would have an expectation of privacy, which would include the entire interior and possibly the back yard too. 

This amounts to lost opportunity because if you had purchased RE, at the closing it can start producing return.5) ADUs detract from the existing structure whether this is privacy, a garage, or just yard space. 6) this is related to the value added by the ADU, but there are many more buyers looking to purchase homes for their family than there are RE investors looking to purchase small unit count properties.