<< One is more outgoing, the
other is more timid. Is that the reason they may not get along well in
the future?

Thanks, >>

I don't think it means they won't get along in the future.  They were babies
and wanted to be together but now they're braver and more independent and have
their own lives.  Do you mean that they are fighting or just not spending as
much time together?  Both are common in cats; sometimes they wrestle around
while playing.  You only have to worry if they seem vicious and act like they
want to hurt each other.

Candace
(take the litter out before replying by e-mail)

See my cats:
http://photos.yahoo.com/maccandace

"One does not meet oneself until one catches the reflection from an eye other
than human."  (Loren Eisely)