Mold problem and mortgaging multiunit

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Hey all, I have a pretty interesting situation in a property I'm looking to purchase. This property is a main house with an in-laws quarters with a separate address. A friend of mine is currently renting the in-laws quarters, and there is an actively leaking roof which has seemingly been happening for years. 

This roof leak along with general humidity has lead to water damage of the ceilings, flooring, trim and a door. There is visible mold and surely plenty more within the walls/ under flooring. 

Long story short, I'm interested in purchasing both units and the 6 acres they sit on. This would be a primary residence (hopefully house hack.) Would the presence of mold, water damage and general inhabitable state of the smaller unit prevent a traditional mortgage legally? I'd say yes if it were the only unit, however the other home is in good shape. 

I appreciate your input.