Don't jump too hastily to this conclusion. They have their usefulness and disabilities.
1. Mitigating factors: They live in a cursed apartment. That place has never worked out for any other couples, either.
2. Mitigating factors: If they are not actors, they have arrived with a huge load of personal issues.
3. To their credit: They offer a good contrast to what we can perceive as "functional relationships." For example, Nora & Kiko don't have sex either -- at least in public rooms -- but we know that they are tightly emotionally bonded and mature.
4. To your credit: Yes, there are absolutely no signs of functional interpersonal communication between Katya & Ruslan. I have not seen it, and that's something that can easily be discerned with even the most distant, casual observation.
Damn, #6. At the risk of becoming unfriended, your Liberal side is showing through. Did bulging cheeks have that much of an effect on your psyche? You almost act like you care.