A week much too short for yr wish-list. Why not more time? You are all retired - you don't have to be back at office. 3 -4 more days, works MUCH better. For 10 days, I'll even plan your itinerary on the spot. How? Because I've done your trip half a dozen times successfully, with newbie companions. Plus I'm a Senior too. To Start, a couple of MUSTs:
1 MUST - FLIGHT -- take a flight that's nonstop from N America (Delta-AA-United-UAE-AIr Canada). Why? These all leave late in day, arrive between 9 -10:30 AM. These are 99% on time, & avoid changes in Europe where delays occur; shortest overall flying time. If you start talking about "my points" then be prepared for longer trips, change-over delays, hassle, just to save a few $.
*2 MUST -SEQUENCE -- Do Athens LAST. After o'nite flight u are too groggy to sightsee busy Major Capital. Instead Reinvigorate in a low-key lovely places, relax, learn Greek ways; u'll then be ready to tackle the Partheon etc etc.
DAY ONE -- ARR 9:30 -10:30 -- allow 2 hrs overlap, get Domestic flight to SANTORINI, arr 1-2 pm. Book Hotel w views; I Personally favor FIROSTEPHANI (locate on good google map)-- Plenty of Caldera-view hotels,away from hubbub of FIra, but easy 15 min walk to its attractions. U can be on yr balcony by 3 pm. Wander along rim path, have dinner w a view (sunset is 6:45 or so).
DAY TWO -- TAXI Or Rental Car by 8 AM to OIA, for 2-3 Hours of enjoying beautiful OIA; when huge crowds invade, leave for other adventures. Museums? Akrotiri? Wine-tasting tour? Another sunset dinner, maybe with music. That's it for Santorini - unless you're archeologists, it's all about the view, and 48 hours is enough to gaze your fill.
DAY THREE -- Fly ATH Airport arr by 11. Get rental car, head for NAFPLIO on modern divided intercity highway (very easy). Just after Corinth Canal, hop off highway 3 miles to spend 1 hr @ ANCIENT NEMEA = overlooked "OLympia runner-up" w. temple ruins and amazing stadium, NO crowds. LAte in Day, stroll & Explore NAfplio Old Town, enjoy splendid Sunset on seafront (better than Santorini!). My hotel pick: AGAMEMNON (One of v few on seafont, fab view, moderate rates, elevator).
DAY FOUR - FIVE - NAfplio, Palamidi & ancient sites. Study BEST website http://www.visitnafplio.com/ - click read EVERY link. For ancient sites, consider hiring "tours by locals"; be sure guides are licensed. And have a swim! Handy beaches & water's divinely warm in Sept. HIghlights of Nafplio & area - http://www.flickr.com/photos/stanbr54/sets/72157632094108982/
DAY SIX - Leave after breakfast drive E. to ANcient EPIDAURUS, mainly for stunning Stadium (15K seats!). Drive up seashore road to ISTHMUS, get off to see CORINTH CANAL. Then join BIg Intercity highway to Airport. Drop car, taxi to center CIty hotel.
DAY SEVEN - EIGHT - NINE -- Explore Athens. A FUN 40-minute orientation for €5 = http://www.athenshappytrain.com/ WIth 4, you might consider PVt Guide for a day -- Acropolis, Acropolis Museum. Check this R Steves site For FREE audio downloads to tour Agora & Nat. Arch Museum. More museums- Musical instruments, Jewelry, Childrens Art, etc. Performances? Dora Stratou Folk-Dance Theatre, Concerts in Ancient Acropolis stadium -- you name it!
A DAY On WATER ?-- Don't do Hydra, please -- long trip in Closed-in Ferry, no deck, no views. Instead, have a 1-hour Greek Ferry Adventure! Taxi to PIraeus, take conventional Open-Deck ferry 1 hr to nearby isle, AEGINA. Enjoy seacape -- huge liners, cruise ships, schooners, speedboats, tiny sloops. Explore town, rent car to visit awesome hilltop temple, beach villages (quick dip?) back to port to wander back streets, then sunset ferry. NOTE - early start or this because open-deck ferrys only @ 8:30& noon. PIX album of Aegina day trip - https://www.flickr.com/photos/36264706@N03/sets/72157621604646139/detail/
That's it! -- you're welcome.