I would say that as long as you don't continuously send the celeb requests asking for autographs you'll be fine. I disagree with people who send request after request just to have more of the same celebs signature. But since you're writing on behalf of your brother, I see nothing wrong with it, as long as you explicitly state that in your letter.

Selise

yeah sure you can

fuck i HATE spammers!!

^STOP WITH THE SPAM PLEASE?

A celebrity won't remember you most likely. I write to some celebs several times.

Edited

I wouldn't think so...I've written to some people over different periods of times about 2-3 times. No more than that though...but I think it would be fine to ask for another. ;)