We will be in Greece next month and would like to know which islands are the best to go to nearby that have dining on the beach for day trips and is Santorini a good island for a three day trip as we will be in Greece for 22 days in order to celebrate Orthodox Easter with family.
More specific information from you would be helpful in formulating responses. You asked for islands "nearby" but did not state where your starting point in Greece will be.
Three nights on Santorini is good but a fourth would be better. We stayed in a cave house in Oia for three nights and drove around the island some (rental car) but didn't really explore Fira or do the caldera rim hike. Recommend Akrotiri, Red Beach and Perissa Beach among things to see/do. Unless you're planning to visit other Cyclades Islands fly to Santorini - the ferry takes waaaay toooo long! BTW - there is a fun beach town called Porto Rafti near Athens airport the locals visit. They have a commercial area right by the water but it may be a somewhat seasonal town. We were there in early April 2016 and some businesses were just getting ready so we kind of had the town to ourselves.
Sorry I meant any islands similar to Santorini but maybe not as touristy although I am not sure How busy It will be in April, are starting point is Athens, I would also like to hear thoughts on other islands that might be as nice and closer to the mainland
No island will be similar to Santorini. Moreover in the Aegean Sea, all the islands are different.
If you are looking for an island not too far from Athens by ferry (2h30 max), you could go to Tinos where there are a lot of things to do and see (but during Easter it will be more crowded).
Or in Sifnos where you will also find the typical Cycladic style. Unfortunately without the crowds of tourists armed with their smartphones to take pictures of the sunset.
In April There will be fewer accommodation options but you will always find someone at the port to rent you a room
Santorini is a great island. It is much better to visit it in April than any other month since it will be less busy and less expensive than May to October's extreme summer months.
We visited beginning of March and most of the places they have started to open.
If you find a hotel on the caldera with a hot tub or pool would be fantastic since it is chilly at night.
We stayed at the San Antonio hotel.