What happenes when one of them downloads and installs a script that writes over mirc.exe and mirc.ini, then adds/removes a slew of other files that can only be cleaned up by simply starting over from scratch? The problem is that most scripts are not user-profile oriented and expect only a single user is making use of the \mirc path.
I'd worry about one sibling's logs/downloads being in any proximity to the other sibling's. All it takes is one little "oops" to start a family meltdown and years of therapy.
