Some people translate the empathic abilities of twins to senses such as smell or sight, which I think is great, because it encourages this idea that they perceive the world in a completely different way than other living beings.
"The sound of a broken heart, the color of sadness"
In particular, I really like to highlight the almost divine nature that Dream and Nightmare have and how this directly impacts their relationships and interactions with the rest, because it inevitably does. Nightmare, at least following his canon, cannot express any genuine or "healthy" positive emotions because it goes against the whole sense of existence, although this is a bit more complex because just as Dream can experience sadness, Nightmare can experience happiness, But unlike this and according to the creator of Dreamtale herself, Corrupted Nightmare is "a thing" that moves by instinct and Dream is his own person with convictions and aspirations.
Dream is the incarnation of something ethereal and beautiful, whose aura is not as aggressive as that of Nigthmare but the way he looks imposes a lot on others. Although I like to joke that he is cute, I think that idea is totally present in the construction of his character. He has to be pretty, pleasant to look at, the light that dazzles you.
I also think Nightmare has that mysticism, but his purpose is not to dazzle, so you could call him ugly even. He imposes himself in a different way, like an uncomfortable sensation that stalks you, like that silhouette that peeks out from the edge of your gaze.