We absolutely have a Levi, who lives next door to Erwin. The two of them hang out all the time (naturally), so it wouldn't be long before they'd all run into each other.

Haha, Erwin knows about the world outside the walls now, but only in the vaguest sort of way. Levi hasn't told him many specifics, and Erwin hasn't pushed for them because he knows it's painful to talk about. Falco, though, he'd have no problem grilling for info.