Would this be a deal breaker for anyone?

[Jessica Brennan]

I have an opportunity to purchase an off market deal, however I'm hoping someone here has dealt with something similar and can give some advice. The house is being sold by the daughter of the man that lived there. However the son lived with his father. Son doesn't work and is refusing to move out. She is from out of state and just in town to close out all of her fathers business. The house is for sale for well under market value because of the problem that the brother is. He won't let anyone in, and she had to get the police involved to just get pictures of the inside. The house was converted, and now has a full apartment upstairs that is separately metered. The upstairs apartment is in perfect condition, the downstairs needs a lot of work. I called my insurance company to see if they will cover any damage that he causes after the house is in my possession, they said they would but I would need to show it was in good order prior to his 'vandalism', but we can't gain access. This also means no inspection. Does anyone have experience with this? Its an amazing deal that I don't want to walk away from (Cap rate 18+%, IRR 67%) but obviously that would change if he destroyed the house.