Have you considered the other options that could work for a family, ex. side by side duplex, house with ADU, house with carriage house, house with a walkout basement, etc?  

There is a carriage house exception but that has to actually be an old carriage house for horses, and from what I understand this rarely applies.

When Laura had a 3 month sabbatical from Intel in Santa Clara she rented a carriage house down on Haskins right there in the heart of historic Charleston. 

HH isn’t just for 20-something singles if the house has a MIL apt,  ADU, casita, carriage house, etc.  

I do not have this in my rental but its something that my wife and I have earmarked as a must have feature of the future carriage house we are building on our current lot, (long in the future dreams). 

If Nashville is like Denver or Colorado Springs where we work, then duplexes are tougher to come by in good condition, so maybe a home with carriage house or separate basement space?

Replacing old carriage beams with new ones (which are straight) is a bad idea, as it will force the whole house to straighten out (and crack the plaster).

I e had people living in my basement in my third floor in my carriage house.

One other option is to house hack a SFH with a carriage house or a basement that has a separate entrance of some kind. 

Most towns/cities in the Denver area allow for STRs in your primary residence -- like house hacking with a basement or carriage house or just a room in your home.