How to do taxes on a development project?

[Lucy Can]

We bought a single family home near downtown Denver, gave it to a builder for constructing a duplex after doing a quit claim to an LLC in 2018. The Duplex finished building in Summer 2019 and we sold it in fall 2019. We got a 1099-S form for our LLC regarding the sale of each side of the duplex. I am using turbotax to file my taxes in 2020. In Turbotax I was reporting the sales under "Sale of Business Property" by reporting the sale price and the basis as the price of the land plus plus enhancements from the builder. I called the Turbotax CPA support to make sure that it is the right place. They are trying to convince me that this is a business and I need file Schedule E with expenses and profit. Turbotax support is claiming that I need to retroactively add the land as an expense in previous tax returns. Further more I need to issue 1099-misc to anyone that has anything to do with the property.

Almost all the work was done by the builder by doing a draw from a construction loan. After the properties went under contract we made some concessions in terms of electronics, smart home equipment, doors and locks etc.

Does it not make sense to file for taxes under Sale of Business Property, since the property was bought as a single family and converted into a duplex? Or do we have to file for taxes using Schedule E for business.

Any help is appreciated.