Romulus and Remus are sister planets in much the same way that Earth and Venus are: one is temperate, the other is hellish.
NASA's Kepler scope has found a system about 1200 lightyears from here with what appear to be two terrestrial-style planets, both in the star's Goldilocks zone. One, massing about 1.4 times Earth, is at such a distance that if it's got an oxygen/nitrogen atmosphere, the average climate would be comparable to Hawaii (thus, probably unbearably hot at the equator); the other, at about 1.7 Earths and in the next orbit out, would be more comparable to Alaska.
So maybe the idea that Remus/ch'Havran is at a distance to have a livable climate on the dark side, and be tidally locked to Eisn, is within the realm of possibility (noting, of course, that if the world is tidally locked, and the dark side is habitable, the light side must be hellishly hot - and living underground would be reasonable, what with the constant hurricane blowing between the day pole and the night pole...).
"Science teaches us to expect -- demand -- more than just eerie mysteries. What use is a puzzle that can't be solved? Patience is fine, but I'm not going to stop asking the universe to make sense!" - David Brin, "Those Eyes"