As a Russian, I've never heard of the name "Eno". But I have a theory.
Arknights loves naming certain characters after cities (Eblana) or mountains (Matterhorn, Monch), and there is, in fact, a Finnish municipality called "Eno".
Even more, it comes from the Karelian word for "river".
So all that may mean Eno comes from either a part of Finland that was occupied by the Russian Empire (which Ursus is an analogy of), or from the Karelia region which is still the Republic of Karelia inside of the Russian Federation (https://www.britannica.com/place/Karelia).
I have never heard of that word being used as a name in Karelia, though.
Another theory I can give is that there exists a Germanic name Eno (https://www.momjunction.com/baby-names/eno/); East Germany was controlled by the USSR for a while, and a part of it (Kaliningrad) still is a part of Russia, which may assume Eno and Sasha were from some Kaliningrad analog in Ursus even if the territorial placement is completely mixed up. Possible with nomadic cities.
But for reasons I can't explain myself I like the Finnish-Karelian theory more. Maybe because they also come from a "snowy" place. Maybe just because I find "being Karelian" more original than "being German".

"Sasha" is a legit name, by the way. It's a short form from "Alexander", and I was very impressed when Alina in Chapter 8 called him "Sashen'ka" which is an even more familiar form, something similar to the Japanese "-chan".