Answers
Although the Greek government has dealt with the issue of the expiration of the residence permit titles and national entry visas with automatic renewal up to Dec. 31, 2020 and Sept. 30, 2020 respectively due to coronavirus force majeure conditions, there is no corresponding directive for tourist type C visas. However, if you are within the 90-day period, there is an established extension procedure for an equal period of time through the submission of an application to the country's police authorities. For better results, you should address your case to a lawyer.
Your wife is accepted as an EU citizen because she is married with you. You must ask from the Dutch authorities to verify this fact and then she does not need a visa.
There is an extension of the validity of national entry visas until Sept. 30, 2020. More specifically, all entry visas that expired after March 11, 2020 will be extended until Sept. 30, 2020. For any other visas not expiring within the above period, the above exception is not applied and the foreigners cannot stay in Greece for more days.