Charlie can't help but think that they could have questioned him while he was in here with Black mere minutes ago instead of dragging everyone around like this and inconveniencing him. He hadn't expected to become so protective over Black so quickly, but well, here he was.
He uses the interrogation – not that it can really be called that – to suggest that Ron and his friends be returned to Hogwarts but is surprised to be shot down.
He doesn't understand why the adults would want three teenagers to be a part of this but hey – at least Harry will be pleased!
Everything Charlie knows about Harry Potter he's learnt from his baby brother, and all of it is concerning at best. This is a kid who makes Ronnie look level-headed. This is a kid who thinks that the things he's done are normal. Ron had stressed in his letters how normal Harry was – and yeah, Charlie can see how it might seem that way if you're living with him but he also knows the truth is more likely that Harry has wrapped normality around himself like a cloak and takes everything in stride so much that Ron doesn't notice how weird everything is. Charlie's missing great swathes of what happened last year but he knows damn sure nothing like that ever happened when he was a student.
But the kid needs a family. That's obvious too. And maybe he doesn't need a family like the Weasley's – a bit too much if you aren't used to them – maybe Black's (and by extension Tonks and their very strange parents) just right for him. Charlie can't tell if that would be perfect or tragic yet.
(Perfect, he hopes, and he really doesn't understand why he wants so badly for Black to be telling the truth. This isn't his story.)