Anniversary trip in May ‘22

The more I do research, the more I realize that just isn’t really possible without feeling like the whole vacation is only packing up and moving

Given the time they have, I believe you have made an astute assessment of what the trip would be, in trying to do 2 islands.

Does he/they want only 'island time', or is some time in Athens to be included in the trip?

Two islands isn’t practical in the timescale.

Does it have to be Greece? For such a short trip, I would be looking to maximise the time on the ground and therefore looking for a direct flight somewhere. Fly into Rome and stay on the coast with a day trip into the city? Fly into London and stay in Brighton? Fly into Dublin and stay on the coast? Istanbul?

United / Swiss Airlines has a flight from Chicago (ORD) to Santorini (JTR) with a connection in Zurich 4h 15m later arriving in Santorini (Thira) early evening.
From Santorini he can take a ferry to Mykonos (2h 15m) and fly home from there. Skyscanner shows an early evening flight on Lufthansa from Mykonos connecting in Munich before departing for Chicago the following morning. Total ticket cost is < $1,100.

Aegina and Hydra.

I like flying into Santorini and out of Athens. We did a day tour from Santorini that went to a volcano and another small island.

Great work from Mary Pat. So it is possible to do this trip.
Of course day 1 is taken up flying so he arrives Santorini in the early evening so realistically he has three nights in Santorini which works out to be 2.5 days. On day 4 the island hop to Mykonos will use up half the day before arrival in Mykonos. Depending on the ferry, the earliest arrival in Mykonos should be around 1pm.
Frankly your brother will just be getting over transatlantic flight jet lag on Santorini and will have a bit of energy for the 2 days on Mykonos before he is going to have to fly home.

If this trip is a must do then concentrate on Santorini only. Fly Transatlantic with connections in Europe both ways.

On Santorini there is sea view which is the north side of the island. Then there is the caldera view which is overlooking where the volcano blew. For the Caldera view be prepared to pay three times the price of a sea view.
For fun here are my images of Santorini
Santorini https://www.flickr.com/photos/stanbr54/albums/72157632154800782

My brother seemed very set on Greece. He has been to much of Europe so I'm guessing he's trying to go for a different experience. I have thought about suggesting island hopping in Croatia or maybe even the south of Turkey, but wanted to give him a Greece itinerary to compare against. I think he cares more about island time than the mainland but I was adding Athens since all the convenient flights seem to be leaving from there. An overnight layover in Munich doesn't work well because then they would be sacrificing one of their days for Germany and I'm sure they won't like that. I see a couple flights that might work from Mykonos but all of them have two layovers which isn't ideal. I also heard Mykonos was a bit of a party island not worth your time if that isn't your scene (someone correct me if I'm wrong) I was figuring 4 nights on one island and then one night in Athens the night before the flight home. My brother is use to work trips to Europe so he knows how to be functional immediately after flying and having little time to adjust for jet lag .

I have looked up accommodations in Fira on Santorni with a Caldera view and although they are quite expensive, I think my brother is willing the pay the premium. He has quite the budget for this trip. Makes me a bit jealous lol. Oia seems a bit out of budget but I do here that Oia is just expensive all around and that Fira is more accessible being close to the port and bus terminal. Would Fira be a good part of the island to stay?

We stayed in a caldera view near Fera and it was wonderful.

We have always stayed in Fira. When we wanted to visit Oia we took an early morning bus. It is lovely and quiet until about 10am when charter tour buses arrive. That is a good time to leave.

While Fira is the main bus terminal serving the whole island, it is closer to the port than Oia but I would not describe it as being near the port.

As for your request for things to do, a visit to the Archaeological site at Akrotiri is highly recommended. Akrotiri is Greece's Pompeii.
Sunset over the caldera is amazing. Its best seen from a hotel balcony however if there is no caldera view from the hotel, we have found one can book a reservation at a cliffside cocktail bar. Time the reservation about a half hour before sunset. While the drinks are expensive you do get an unobstructed caldera view and a seat.

Yes, Fira is right smack in the center of the Caldera making it close to Oia. Your brother may want to walk around this area and then work his way to a restaurant that offers a sunset view. I would definitely make a reservation and allow time getting there in case he needs to hop in a taxi to find it. This island is jam packed just before sunset because everyone is trying to find an amazing spot to watch it.

If they are staying near Fira, one "sunset restaurant" i have enjoyed 3 times with newcomers to Greece is the top floor terrace of STANI Taverna. http://www.stani.gr/ It is 1 lane back back from the cliff-edge promenade, but because it's higher, and 3rd floor, it overlooks the rest with a lovely clear view. I usually stop by the place the morning of the day we plan to go there, & clim up the stairs to the top & talk to the staff there. I point out the table we'll want, with th best view, and promise to be there Promptly at 7:30 (in May, sunset is about 8:30, but we take our time about ordering... and have our cocktails there, befoe dinner). NO $$ "sweetener" is needed (unlike situation elsewhere & in high season) and they've always held our exact table. You can have your hotelier mark the location on a map -- since Santorini (and most greek villages) don't have street numbers, or often even street signs. OR you can have your hotel clerk or landlord call whatever restaurant you choose, for a reservation. They should also add that it's a 10th anniversary -- don't be shy, they'll treat you special; you deserve it. They serve traditional Greek food, and if you are looking to splurge with a $100 dinner bill, you're out of luck --- we have often ordered dish after dish, and More Wine, but never have managed to spend more than about $25 per person including wine.

Or As Stanbr suggests, you can split your evening, drinks in one place with best view (book a table in advance), then dinner in another. We've enjoyed a stunning view at VOLCANO CAFE, rooftop terrace, right on the 1st pathway at north edge of Fira

I've recommended looking for a cliffside hotel with balcony view in FIROSTEPHANI, which is on N Edge of Fira town... close enough to walk easily in 15-20 mins to heart of Fira town, but very serene of evening & never invaded by cruise or pkg-tour armies. A dinner with great view right there can be had at REMVI Cafe.

I think solution for View within budget, may be Firostephani. browse with https://www.booking.com/city/gr/firostefani.html click the upper RH icon "Show on Map" to see the "balloons" for all available places in their EXACT locations - v. handy because sometimes on own websites, hotels "pretend" to be on the Caldera. They also can say "ocean view" which really means a view to the eastern shore of the island; look for "Caldera View or "Landmark view". Also look only at hotels to the LEFT (West) of the main N-S road (called 25 Martiu) ... because the terrain slopes steeply downward to the east of that roadl. I just now entered "dummy dates" for the weekend of May 13-14-15 and saw availabilities at several places I can recommend -- you haven't shared $$, which forces us to guess (always good to state budget range when u ask for good advice) -- but I see caldera-view balcony double rooms @ Hotel Mylos for $346/3 nights, Remvi suites pvt suie @$689/3 nighs, Agali Houses $848 - u could also check Agnadema Apts, same area, caldera view from pool. Of Course in the same area there are rooms for $1400-$2100 for 3 nights if that's what he wants... I just wanted to show examples of good views, affordably, in comparison with OIA and parts of Fira. I'm familiar with all of these too.

Janet-

Hello fellow Philadelphian! Thank you so much for the wonderful advice, that was all extremely helpful and gives me a lot of direction. My brother gave me a budget of around $8k to include all the money they spend on the ground in those 5 days so its not a very limiting budget. I worked it out to be around $5k on accommodations, $1.5k on food ($150/p/d), and $1.5k on spending/activities. If I could shave $2k from that budget I think I could convince him to allocate that extra money to the transportation budget and upgrade to business class flights. Which for a 6'7" guy like my brother with a wife who is 5'10" (who has never flown business class before) I would think is worth the cash. So the first budget I gave to myself when looking was $3k for 5 nights accommodations. Which seems to still leave my options pretty open. But let me know if you think my activities or food budget is too low.

Chris have sent you a PM because my computer is acting up today

I will recommend you to check the combination of Corfu and Paxos island. I think that it matches your criteria and will really enjoy it.If you need further information do not hesitate to contact me.