Worrying about him won't help whatever is wrong with him. But u don't need to fake smile either. Ask your parents of even his doctor if there is anything u can do to help him when he's released from the ICU.
If u aren't worried of upset don't pretend to be, just don't be mean of in-sensative. Just do whatever u think is right don't pretend u feel one way if u feel another. btw sorry if I sound mean of anything, but why is ur brother in intensive care. (If u don't want to say u don't have to, u could always inbox me otherwise if u don't want everyone to see. Anyway if u can't say I'd understand)
Be realistic about it, but not too realistic. Be as optimistic as u can about it. Having an optimistic attitude will help u be happier,and there's still hope for him. And also, if u feel like crying, then cry. U sometimes just need to let it out. :) I hope this helps.