Thanks to all of the comments thus far, I have come up with the following itinerary and need feedback.

Arrive in Athens June 10 and take a plane to Chania
2 nights in Chania
1 night in Heraklion
Ferry to Santorini for 4 nights
Ferry to Milos for 3 nights
Ferry to Sifnos for 4 nights
Ferry to Athens for 2 nights
Fly home

Main concern is perhaps not enough time in Crete and too much time in Santorini? Your thoughts? Should I eliminate Milos?

I should add as a reminder - we are a family of 4, "kids" are 19 and 15. We typically go for places with interesting sights as we are not lay-on-the-beach kind of people. We love good food, snorkeling (though I don't think any of these islands are big on that)

Santorini is more of a "sit-back-and-relax sort of island so you might want to add one more day to Milos unless you're interested in Santorini's nightlife.

I would take the day saved from Santorini and slap it on to CRETE ... that island is an Entire Country .. with one more day, driving from Chania to Heraklion could be a "blue highway" adventure... go the "old highway" inland route through Episkopi ,,, find Argyropoulis (water pours out of the mountainside) and stay all night at a pension near the ruins of Lappa -- and THEN go on to Knossos & Heraklion.

I liked Milos OK for 2 days ... it's mainly a beach destination unless you're up on its great archeology ... food is far better in Sifnos if you ask around (try Maganas in Artemonas).

If you're not lie-on-beach people, maybe you should jigger it around so you have 1 more night in Athens? Take the "400" hop-on/hop-off tourist bus that Athens has finally got round to running... it will take the boys to the amazing buildings of the Olympics. Check out ALL the ruins... and what about the Musical Instrument Museum? the Goulandris Cycladic Museum? Did you know there is an entire huge jewelry museum? Think about going up to the top of Lycavettus Hill (the OTHER hill) to look at the Acropolis at sunset... there's a funicular that goes up there. Lots of stuff.

We loved Crete so much that we literally had to tear ourselves away after two nights- assuming that your Heraklion night is for the purpose of Knossos and the ferry. I really wanted at least another day to drive to the other side and that pink sand beach (we hiked the Samaria Gorge our one full day). Our teens were only a little younger than yours at the time. Santorini seemed to me more toursity, clubs at night and sunning by day, albeit just gorgeous, which is why I agree with your second thoughts about adding, instead, another Crete night over the 4th (and possibly even 3rd) night in Santorini, based on your familiy's interests in more active things to do. I also agree that you might want another full day for Athens, although this might depend on your group's interest in archaeology and mythology. I highly recommend staying in the Plaka district if you haven't already made your hotel reservations- they will have a great time wondering on their own there, if they need some time away from you

Based on suggestions, how does this look?

10 June. Arrive in Athens and take a plane to Chania-Crete.
10 – 14 June. Spend 4 nights on Crete (2 in Chania and 2 in Heraklion) .
14 June. Take the high speed from Heraklion-Crete to Santorini. Depart at 09.45 arrive at 11.50
14 – 17 June. Spend 3 nights on Santorini.
17 June. Take the ferry from Santorini to Milos. Depart at 8Am arrive at around 12.30PM.
17 – 20 June. Spend 3 nights on Milos
20 June. Take the high speed from Milos to Sifnos. Depart at 1.50pm arrive at 2.30PM.
20 – 23 June. Spend 3 nights on Sifnos
23 June. Take the high speed to Athens. Depart at 12.20 arrive at 3PM.
23 – 26 June. Spend 3 nights in Athens.

I realize the ferry info is speculative.

Looks pretty good to me ... and you'll be able to firm it up when the ferry schedules finally come out in late April or so, for June.