Did you do an inspection? If so, what were the results?
To "unwind" the deal, you'd need to show that the sellers *knowingly* misrepresented the issues with the property. This is a VERY hard hurdle to clear - black mold? We didn't know about that, sorry. No permits? We didn't do that work, it was the previous owners, etc.
I was actually sued once by someone who bought a house built in the 1800s (and remodeled/added to many times since, through probably 15 different owners) and 6 months later found asbestos debris in the crawlspace (we're talking _crawl_) of the oldest part of the house. The stuff had probably been there for 50 years, and since we'd never entered the crawlspace, there was no way for us to have known about it. The judge literally laughed the suit out of court and dismissed it with prejudice.
Now, if you have incriminating emails between the seller and her realtor talking about hiding the black mold with spraypaint and duct tape or something, then you have a case. But I doubt that. You have to prove that the sellers *defrauded* you and lied.
The bottom line is that it is *really* hard to win a lawsuit in your shoes, which is why you do a crazy amount of inspecting/due diligence before closing.
Fix the problems, consider it a lesson learned, and go on with your life.
-W