About Easy Cruise --- sorry to have to rain on that parade, but E-C after a promising start, turned terrible. Many bad reviews on TRip Advisor. com and cruisecritic... it seems they couldn't make money on their original premise so the services were cut back sharply, they began REQUIRING people to take meals, and serving really bad food, their schedules went wack ... you name it. Man unhappy people. I think the line was sold during this year.
That being said, if someone wants a person/agency to take care of all the details, I agree with those who say, let a GReece-based agency handle getting yoiur hotels, flights, ferries, and having cars take to you/from Ferry or domestic plane. Dolphin-Hellas or Thesaurus travel have had the best recent reviews in my opnion.. Fantasy may have outrun its past rep.
The way to get what you want is to come to such an agency with SPECIFICS ... you want to pay no more than xxxx per night at Island ____. You want to be at the beach (??) or in town in Mykonos, in Santorini you want accmmodations (1) in perissa or kamari beachtowns or (2) in Caldera towns -- Oia, FIrostephani, Imervogli or Fira Town (do a little homework and decide first). If u are going to Crete be sure u have at least 4 dys for it... Don't stay East of Iraklion unless u can afford (and want) posh resort accoms at Elounda ... Most efficient way to visit is to fly or overnighte ferry to Chania area... then tdravel south/then east &north to Heraklion area for ferry to Santorini... a classic triangle that all of us crete-lover use... look at a map & you'll see why. This can be done on public transit, or by car rental.
Of the 3 islands u list, only Crete will give u much contact with actual GReeks and how they live (assuming you want this; some mainly want to sun, go to spas, buy jewelry and leave). In that case, Mykonos and Santorini can be done without meeting many Greeks at all. But one would miss a lot.