Phaeton siblings

While Wise and Belle has interchangeable roles in story as the MC and the sibling, there seems still instances that the MC and the unchosen sibling are treated differently...

But what exactly are those instances? Like things that the only the MC knows while the sibling is left in the dark, or the MC can do that the sibling can't (or at least not seen doing on-screen), or how the other characters treat the MC compared to the sibling?