While they do look alike, that's not them. First of all, check out Pixiv tags, second of all, the artist really likes those two so that's them. I can understand the confusion though. If not for the tags, they would kinda hard to identify because pic is monochrome and sketchy.
I can't as I don't have a pixiv account to see R-18. In this case though I'd have to argue that the tags are wrong for some reason.
I'm going by the hair being wrong for it to be Sanya and Eila, Eila never wears a (British/Btitannian-style) sweater, and various details related to their bodies/character designs that are consistent with other art of Elma and Beurling..
A post with a similar pose, by the same artist, of Sanya and Eila. post #1171466
The sweater is Beurling's. Problem with mass uploads like this is that the artist doesn't always tag every character (post #1277083, for example, isn't tagged).
