How to determine "Duplex or guest house" and appraise the value?

[Jesse Zhu]

I am analyzing a deal in Valley of Enchantment San Bernardino CA. Two houses on one lot with two different street #, one larger (2/2) and one smaller (2/1). The title report shows the total square footage, total room of 6, but only 2 bd and 2 ba, but not as two units. 1. How to determine if it's duplex or guest house (zoning is SFR) 2. How to value the deal if there is lack of 2 unit comps in the area? Can I just appraise the total square footage and bd/ba counts? Any thoughts or comments are appreciated.