Assorted comments about stops en route etc.
ANCIENT CORINTH -- r u really interested in this, or just because it's on the Highlights list? My friends have enjoyed it but they take things slow & are in early 60s. May be a lot of walking among ruins for parents if they're in 70s & get tired. U need to read up on this. An alternate stop, shorter & more level, en route from Nafplio to Delphi, is ANCIENT NEMEA. It's a "Olympia wanna-be"... the runner-up for Ancient Games. It's just 5 miles off that big highway s. of Corinth ... and is delightful. Has columns of ancient Temple, a good SMALL Museum, beautiful grounds (it was excavated by Archeologo Dept of U Cal Berkeley, so they have the$$$). Also, separate (u drive down road 1/4 mile) a STUNNING stadium! SO much is just as it was... the hero's tunnel... the stands.. even the original starting blocks from 2400 yrs ago. The local area was inspired to Revive the Ancient Games, and in JUne they're holding the 7th REvival... thousands come from around the world to dress in white chitons and race for laurel crowns. I have brought newcomer friends there 2x and they were all thrilled. http://nemeangames.org/ tells about archeology ANd games.. a restful stop
DELPHI - I don't think you need 2 full days unless you want to seek out some churches ... you can come in early afternoon, see museum that day, Day2 @ 8 am, see the ruins part. I understand your wish not to tire your mother too much, & here's my thought. the road into town is uphill & steep .. first you see the AThena Temple, then the Ruins site/temple. KEep going.
You should continue uphill to the "village center" -- really an intersection of an upside-down Y, u are comingin on one arm. Park & find hotel. We booked PAN hotel about 100 yards downhill from intersection. (funny story, hotelier said, we have nice rooms on this same lobby floor behind lobby. We said ??? show us. Walked down corridor into room, out on balcony. Hawks were circling -- 100 feet BELOW us (!)... sheer drop down mountainside, view out thru olive groves to a silvery sea. I said, we'll take it). It was 5pm (if u are earlier, parents could nap an hour). Our landlord said, why dont u got to museum before dinner? It's empty this time. We walked down road, a sidewalk beside the parapet, flags flying, vie down mountain, gorgeous. Museum is WELL-signed easy to understand no one there, enjoyable. It's about 1/2 mi walk at most, downhiil... but 1 of you could walk w pop, the other drive with Mom. At that times, easy to park by site. Then all 4 of you could drive down to Athena Tholos, then back uphill to village center for sunset dinner on a terrace.
Morning of Day 2, be there at 8? 8:15? opening time to tour ruins. Bus crowds don't arrive untiil 10 am or 10:15, by that time u will be higher up on ruins (you walk uphill into them). Don't attempt to go all the way to the top where there's a stadiium because u can 't get in, due to recent rockfalls; (they r afraid rocks will hit tourists who will sue). En route up, there are plenty of low stone walls where one can rest; i know I did. YOu can really benefit from a pvt tour -- there is one in Delphi who is (justly) famous for knowledge & presentation - Georgia Hasioti - http://www.delphi-guide.gr/ her fee is about €60 per hr/2 hr min; she meets u at site (this fee is usual rate). Do not delay in booking - she is sublime & in high demand. Afternoon u can go on to that monastery or, if parents are exhausted, just stay another night
Final tip I give to ALL going to Delphi -- Drink the Water!!! At a simple "diner" terrace, waitress filled glasses from a pitcher; I tasted & gasped; BEST water ever!! I said, what brand?? She said, straight from tap. She pointed up at the mountain above us & said, it comes straight from the snow-pack on Mt Parnassus (the famed Mt of Inspiration!) Next AM before leaving we filled our backpack bottles.