IMHO (and the Avast team are the best to confirm this), you would probably be better off by registering your second copy of Avast Home seperately and not to use the same registration code for both.
My theory being, when your PC(s) are checking the Adwil servers for updates, you might get a problem with the two PC’s returning different details to servers. ie the Adwil servers might wonder what the hack is going on if they are presented with the same registration code from two seperate PC’s.