Edmund does understand. His relationship with Peter had been difficult, once, but after fifteen years of ruling together, of being the High King's right hand, Edmund's relationship has long since been patched. He remains calm because the Just rarely panics, even when there's nothing to be done about a situation.

"Stay here tonight," he suggests, and it's very different from a command. "I'll take Destrier and go out, and keep searching for him." You need rest, are the words Edmund doesn't say. "The girls need one of us to be here." That's not precisely a lie, but it isn't the strict truth: Susan and Lucy are both more than capable of holding it together, but Peter would have liked one of them to stay with the girls; not because they're girls but because they're his little sisters.