In one of the few continuity glitches for Londo, we never hear from his nephew Karn again (which is why my fanon is poor Karn committed suicide after being called back to Centauri Prime because of his forced speech)

That makes a disturbing amount of sense. Otherwise, you'd expect Londo to be advancing his career later on when he goes up in the world.

Also, not only do we never hear from Karn again, but his existence implies that Londo has a brother we never hear a single thing about. Londo is the head of the family, so either his sibling is younger or he died young.

Either way, I suspect he's dead by this point given his conspicuous absence in this episode. If he was alive, you'd expect Londo to mention him.