Both the S corp and the regular C Corporations are required to file an annual corporation tax return. According to the IRS it is immaterial if the business operations are either minimal or non-existent.
Generally speaking, for both the 1120-C or 1120-S Corporation tax returns, there would be no corporate income tax liability. However, on the State Corporation tax returns, the Corporation may be subject to the Franchise Taxes applicable to that particular state.
So, ignoring these State Corporation Tax returns may potentially subject the corporations to additional fines and penalties applicable to that particular State.
I would suggest that you file these corporate tax returns and have your CPA eventually dissolve these corporations to avoid these future State Corporation Franchise Taxes.