The two Estonians are like two peas in a pod, and other clichés which indicate they're like twins. We'll refrain from calling them Ashley and Mary Kate though. Actually, the two Estonians are practically like one person. We only learn the name of one of them, when Shukhov addresses "Eino" when asking for a cigarette (516).
The two of them literally do everything together, and they even look alike.
They were both tow-haired, both lanky, both skinny, they both has long noses and big eyes. They clung together as though neither would have air enough to breathe without the other. [...] They shared of their food and slept up top on the same bunk [....] they never stopped talking to each other in their slow, quiet way. (260)
But these two men aren't brothers at all; they met in Gang 104. The two Estonians really stand out for their extremely close relationship. A major theme in this book is competition, and we see a lot of ruthless behavior among the zeks, who all mainly look out for themselves only. The two Estonians work together cooperatively though, which is a very different survival strategy. But their strategy might be just as desperate as that of the zeks who compete on their own against others.
In the above passage, Shukhov mentions how they "cling" to each other, as if they couldn't "breathe" without the other. This could be the cue for a cheesy power ballad. But it's also a sign of how trying and awful camp life is. Even the close fraternal relationship that these two men share has been impacted by the camp; their close relationship is largely a product of their fight for survival and their need for some sort of solace, or comfort, in the bleak world of the gulag. Some good can come out of even the gulag though, and the family-like relationship that the Estonians share is one of those things.