Since there are 4 of you, I agree that Laura of RS is right; 4 bus tickets same as car ... just be sure that 2 in y our party get those International Driving permits, then you can trade-off driving. Rick's guide probably follows the itinerary of his group tours... however you shouldn't get ambitious & try to cover all that bus tours cover ... because there's a paid driver for those, so the tourists don't get tired! I have never tried to do these 3 at once. But here are my comments AND my fave online map http://euro-map.com/karty-grecii/peloponnes/podrobnaya-turisticheskaya-karta-peloponnesa.jpg (click & it gets huuge)
• SEQUENCE - I would say Delphi - Olympia - Nafplio... maybe Laura has better thoughts.
DELPHI -- Start By NOON - takes 3.5 hours to Dellphi. Check in hotel (I loved PAN - back rooms look down mountain to sea). Walk the Rimside path to Museum by 5pm -- NOBODY will be there! then downhill to Tholos tomb before sunset (Drive the latter if you are tired.) Dinner & early night - get to Ruins site by 8 AM, you'll have it to yourself for 2 hours ... DO some homework (good guidebook) to interpret what you see, or hire local guide for 2 hrs http://www.delphi-guide.gr --when tour-bus mobs arrive, you leave...
OLYMPIA -- I guess the way would be to go down to shore, & over the Rio bridge and the expressway around the west rim of Pelops to Olympia. I got a very budget hotel, Hercules, you may find a better one, the main street is just Hotel Row. Get to the Site at 8 AM. Best tip I got -- go to museum FIRST!! Nobody's there, you can focus. By 9:30 the bus mobs pour into Museum, then you go out to the ruins, plenty of room to rove ... by Noon, you're ready to leave.
NAFPLIO -- I would use https://www.viamichelin.com/web/Routes as a route planner ... several (mountainous) routes to reach Tripoli, then it's smooth to Nafplio, Probably by 5 pm? Wonderful sunsets, they'll make you forget Santorini totally
-- Next 2 days... your choice of NEmea, Mycenae, Tiryns, Nafplio old town of course -- and swims! I like the tiny cove of Asine/Kastraki instead of CRowdy Tolo beach... only one taverna there, and Super for a seafood dinner. On the day you head BAK to Athens, go across the "thumb" of the Pelops hand, to see Epidaurus on the way, then go up the seaside road to Isthmus, stop to take pix of the Canal, then get on the Big Intercity highway again to Athens area. If you want to avoid city's hellacious traffic, y ou can drop car at airport & 4 of you can taxi for 38E to your hotel.