If Lied was the little brother, he would be the little brother that 100% believe his brother cannot live without him. Iruma would be that airheaded older sibling that everyone adores but would get serious if his little bro needed help.
On the other hand, if Iruma was the little brother, he'd be both babied and corrupted (attempted at least) by his big brother. Lied would be the parents example of what not to become from the sibling standpoint, with Iruma having a low bar to surpass.
I love both of these fictional set ups, but Lied as little brother is fav 💜