Two big causes of moisture I have observed are tenants running humidifiers and not using exhaust fans when in the shower (make sure your bathroom has an exhaust fan).

OR tell him the property is already sold, and maybe just structure the whole thing as if he has no choice really, it's all just "After-the-fact" Stuff...?

One issue will be if you are buying a townhome or condo in those areas, most are legally structured as condo's and FHA has restrictions on condos will limit the developments you can purchase into the ones they have already approved. 

Its a townhome- 4 bedroom, 2 bathroom, 2 kitchen unit. seller sais its set up as a two unit. 21944 sq.

Zillow has no idea if you just did a $200k renovation or if it's structural unsound.

there were all sorts of fires.. turns out they would use the sink in the bath room to put briquets in them and put a BBQ grate over it and cook their chicken skewers.. 

Fairly common structure that has been discussed on the BP podcast many times. 

Bathrooms and kitchens get the modern treatment.

What are some suggestions on how to structure this deal ?

@Emanuel Vega you seem to understand the basics about the LLC so I will leave it to an attorney to talk about how to structure things.