A CTL-U from within RM will reset the RM product registration key on one of your two computers. At this point, you can enter your other product key so that one computer is running on one product key and the other computer is running on the other product key. That way each computer can have their own separate account at myrootsmagic.com, which is the need your household has that needs to be met. And after all, you have paid for both product keys.
CTL-U is a rather global reset, so after doing so you will need to re-establish things like RM's default folders and any saved passwords. But it does cause any data to be lost.