Mrhand, I answered this before I saw your post about Santorini, and your wife's limited mobility with bad knees. (I can sympathize, since my left knee went bad, luckily my "titanium joint" has worked perfectly for 5 years, with no pain!). That information makes me think you should really research some sights --- Mycenae is on a high hill, and you must walk up steep inclilne to even enter the fortress, and there is MUCH walking on steep paths there. First time I was there, 20 yrs ago, Crowds poured out of busses, but I saw many left behind, sitting under trees with their canes... paid all that money for tours & were not mobile enough to see ruins.
There are options to consider -- en route to Nafplio, you might want to stop instead about 10-15 miles beyond Corinith Canal... RH side, exit to ANCIENT NEMEA (The "runner-up" to Olympia as Games Site). It has towering temple colums, a nice museum (all thanx to U of Cal Berkelely), and an amazing uncovered/discovered Stadium. You can drive right up to entry to both of these. Nafplio is very enjoyable even for the less mobile, because the Old Town main part is level, and if you can book right hotels, great views from balcoonies. Hotel Agamemmnono is BEST location - one of the few right on Seafront with seaview balconies (good luck & book NOW). It even has elevator! (unusual)... and is moderate price compared to others. A luxury hotel.,Ippoliti, has good location and a rarity in Nafplio, a pool! -- this may be important in July for your wife; for your other couple, there's good swimming nearby also). I suggest you spend at least 2 full days in Nafplio... much to see & do, restful evenings sitting in marblepaved mailn square under the trees, in moonlight. Instead of Mycenae, just outside Nafplio is ANother Iliad-era fortress, with NO bus crowds, TIRYNS. itl's not restored, no museum, but just one steep path to top which is all level. VERY impressive, can be enjoyed in 45 mins or so.