"You are turtles."
Translation:Εσείς είσαστε χελώνες.
Είσαστε & είστε are different types of the same thing. They both mean you are (plural) and are interchangeable.
does it have to do with politeness? Are both εσείς είστε and εσείς είσαστε correct?
eiste is just a slang way of saying it. Σαν "θελεις" και "θες" ή "ξερεις" και "ξες"
Now you are just trolling those people who pop up saying "BUT WHEN WOULD I EVER USE THIS SENTENCE!!1!1!!"
Don't get fooled by troll1995's username, we're trolling no one in these discussions. :P Mostly because, most of the times, people who are very displeased with weird sentences, are also rude towards moderators. Trolling encourages negativity, which is something moderators are not very fond of when trying to keep the forums user-friendly. :P