well, it imply he know because he mentioned about posion but he never confronted the evil wife . Just like the posion sweet , the old man couldn't believe Norah's mom would do such a thing until the evil wife confess it was her plan & he was piss & said he knew it , only she is stupid & evil to do such a thing . I believe he know but choose to turn a blind eye. I'm not sure if the evil's wife is the step-sister but the dad ( cripple man ) said the older sister was a kind person who loved her but she kill her coldly b/c of jealousy & greed. The evil wife hate Norah's mom b/c the irony is , the evil wife is the Mistress , who commit adultery while Norah's mom is the legal wife and intitle to half of the old man wealth! Even though Norah isn't the real daughter but she is registered as his daughter & bear the last name , which mean if the old man would die , all wealth goes to KK & Norah, leave the evil 's wife out.