3rd unit being rented in a duplex uninsurable?

[Jonathan West]

I am looking at acquiring a duplex in Milwaukee.  However, there is a 3rd unit (finished attic) being rented to another party.  There is only 1 exit from this unit.  Is this illegal?  Will I be able to get property insurance with this tenant in place?  If I am able, will the insurance be void if I ever have a claim on the insurance? (fire etc)  Lastly, can I be personally liable if there is a fire etc in the unit?  (I assume yes).

Good purchase price, lots of potential issues.

Thanks in advance everyone, so much more to learn here at BP.

Jon