Can we hold the seller responsible for inspection problems after the sale?

You can sue the seller for fraud for failure to disclose the mold and sewer problems.  You can also sue the seller for fraud for the phony home warranty.  You can sue the seller for misrepresentation for not following through with the termite inspection.
You can sue the inspector for negligence for not discovering the mold and sewer problems.
Fraud is the intentional misrepresentation or nondisclosure of a material fact made with knowledge of its falsity and with the intent to induce your reliance upon which you justifiably relied to your detriment.
In other words, you would not have bought the house had  you known its true condition.
Damages (monetary compensation you are seeking in your lawsuit for fraud against the seller) would be either the benefit of the bargain or your out of pocket loss.
Benefit of the bargain means a defrauded purchaser may recover the difference between the real and represented value of the property purchased regardless of the fact that the actual loss suffered might have been less.
Out of pocket determination for damages for fraudulent misrepresentation permits recovery of the difference between the price paid and actual value of the property.
Negligence on the part of the inspector is the failure to exercise due care (that degree of care that a reasonable home inspector would have exercised under the same or similar circumstances to prevent foreseeable harm).  Your damages for negligence would be all costs, expenses, and other adverse consequences caused by  the inspector's negligence. 
You would file one lawsuit naming both the seller and inspector as defendants.