How do I enter information for 2 houses on 1 property?

My house is listed on Zillow.
However, there are two houses on the property.

It is one lot with two houses,
the second house is traditionally called "in-laws quarters."
The 2nd house is not listed.

Many of the homes in my neighborhood
have 2 houses on the lot.

How do I factor in the 2nd house into the Zillow listing
under the address of the main house?
Do I simply add the number of bedrooms, baths, etc?
. . and then, add that it's the 2nd house under additional information?
wouldn't that be misleading?
and the Zestimate number would be less than accurate. . .
So, how do I do this???

Please know that it would NOT be another listing.
Per the zoning in the city where I live
the houses cannot be sold separately.
So, how do I make sure the 2nd house's information
gets listed/attached to my property here on Zillow?