Running comps for a property with 2 houses

[Christopher T]

Hello everyone. I am negotiating for a property that has two houses on it. The other properties in the area only have one. The main house is about 1000 sqft and the back house is about 800 (has long term tenants paying $1,500 a month). Comps in the area for 800 sqft are about $420,000. How do I account for the extra house in the back when I make my offer and, if accepted, when I advertise it to buyers (planning on wholesaling it). Thanks!