The other 3 children, including the one with the POA want Grandpa out of the toxic environment.  

Now, you as a landlord maybe the nastiest racist white trash on the planet, or you maybe the most even handed Democrat voting metrosexual attempt of a man, if you disregard the eviction record of two white tenants, how do you justify denying the third application from a black man that was evicted at some point?

The best students on the planet are law students.  

Before you start singing praises for certain companies and what they sell you might find this interesting....http://saferchemicals.org/newsroom/new-study-finds-toxic-chemicals-widespread-in-flooring-sold-by-top-retailers/

Now I'm realizing that for this whole idea to fit in line with my values I'd really like to use my investing to not only create a passive income for myself but also to contribute to making low socioeconomic urban neighborhoods better, particularly for kids who grow up in those areas, like helping them be less exposed to toxic substances and pollution, or have safer neighborhoods to play in, or more access to health/education resources. 

I fell for every sob story on the planet... if it was me I would told him no problem to just get him to shut up and get off the phone..

What about household chemicals which are considered toxic or flammable , will these be considered a breach of lease?

Sometimes tenants start doing this when they want out of a lease for any reason on the planet.  

For one, she accepted the place "as is," and secondly, she'd have to prove this mold was toxic, etc., which is very unlikely.So, if I was you, I'd get my lawyer to start the foreclosure process. 

I agree, if he's this rude to people on a forum trying to answer his questions I can only imagine his toxic attitude towards tenants who don't live up to his standard of education or intelligence and dare to make a complaint.