I would view this as a 2bd/1ba house with an outbuilding (like a shed) on the property. Based on what you're saying, the second house is uninhabitable so I wouldn't place much value on that at all. I actually own a property almost identical to what you're describing, but both units were functional when I purchased them. I pay the water/sewer/trash there because they are not separately metered. It could be pretty costly to wire that other house and you said it needs other repairs, so that's why I wouldn't give it much value. It's a storage building until you finish it out.
Just my opinion.