Two single family homes on one lot

[Christopher Jason Lloyd]

I have two single family homes on my property and the MLS has it as a duplex. The tax records have both single family homes as improvements on the land. My concern is that I am in a district zoned for single family. I am looking to possibly rebuild the second home on the lot but don't want that to impede my non-conforming use of the property. The homes were built in 1950 and 1952 and are metered together. Has anybody ever been in this situation and know what I can and cannot do with this property? Thank you.