I could vote for Milos as a good adventure for 3 days ... especially if you are fond of swimming and boating. Milos has a fascinating port town -- a huge HUMP right in the town I couldn't figure out... Learned later that Milos was a volcanic island, causing such odd protrusions. Do not miss the tiny but Fascinating Mining Museum... AND an unforgettable 30-minute documentary about the Milesians working in the mines ... for 2,000 years this islnad has mined, up to the present. Be aware, most of the cafes & nightlife are in the port town, but the beach there is well, meh. The island has I think 22 beaches, some are great fun, but the public bus system is lame so you'd have to rent a car for a day to explore.
Then on a 2nd day, sail around the rim of the island... the boats on hire line up at the harbor before dinner & you can visit, talk w. captains, and choose. Our options were a small 6 psgr sailboat doing full round-island, or a catamaran, large, doing half-round. 2 of us tried a smll boat, 3 of us tried the cat -- and latter had the BEST time... despite winds we were under sail 75% while small boat just motored... and our vessel had enough time to stop for swims & a barbeque, and rubber-boat rows thru a weird cave.
If yr husband mandates Athens first, he should face the higher cost & more transit time that results. If one arrives in Athens & then transfers quickly (a 2 hr window) to a domestic flight (40 - 50 minutes max) to the farthest island, then one can "hop" back with 2 - 3 short ferry trips. Athens 1st = precious time lost, maybe more money too. Here are options to isles if AFTER Athens --
• FERRY to Milos June 23 - the only DAILY ferries are at 7 or 7:30 and take 3+ hours with 2 stops. These are not the large Blue Star, with decks, but are all-reserved, all inside seats no decks, no walking around, not great with kids. Adult ticket is $70. Additional cost = $20-25 taxi from Central Athens - Pireaus. and Breakfast $ on board. The only other sailing on Wednesday is the ancient "lifeline" rustbucket, 7 stops 8 hours.
• FLIGHT from ATH - Milos June 23 == Earliest 8:40-arr 9:20 (40 mins) @ $103 adult fare. midday fares higher, the 6-6:30 flight is $92. Additional cost: €38 flat-fare taxi to airport.
• FERRY to Paros June 23 - the Blue Star leaves 7:30 - arrives Paros about 11:30. Economy fare only entitles you to seating on deck in plastic garden chairs. Reserved seating $50. Additinal cost: $20-25 taxi fare from Central Athens - Pireaus. + breakfast on board
The fact is, if you don't connect at beginning, straight from airport -- you don't find "great ferry options". The majority of daily sails start EARLY in the Morning & then again late afternoon (Note: this is mainly because ferry schedule to/from Athens is set up to serve the needs of Greek citizens who live on these islands, not the tourist preferences). So you have to "go with the Flow"
I know this doesn't solve your problems, but perhaps explains why trip planning & sequence strategy is an art. if your time or budget -- or both -- are limited.