Set all users' $HOME to /var/www and use system-wide aliases

If you just need them to start their sessions in /var/www by default, you don't want to change their $HOME (which is a bad idea anyway since /var/www won't belong to them). A much cleaner approach is to add this to their ~/.profile files:

cd /var/www

As for the aliases, all you need to do is modify their ~/.profile files to source the alias file you've created. Add this line to each user's ~/.profile:

. /path/to/.aliases

This way, they'll move to /var/www each time they log in (since login shells load ~/.profile) and they'll also have access to the aliases defined in /path/to/.aliases.