I purposely had him not say a lot, because I wasn't quite sure what he'd say. I could put something like that in there. ATM he does seem too calm about it, but since it's in his POV (3rd person) I do have him in his thoughts being upset.
Okay, as for Ron dealing with the news that one of Ginny's twins has died. I think he'd be in shock, but not emotionless. Ron tends to react very quickly to things. He cries/gets angry immediately following Fred's death.
He'd be shocked and probably show this. I think he'd be supportive as well, but probably say something very tactless like 'at least the other one's all right.'