Newbie Question! Have 2 MyBookLive HDs but Windows only shows contents of one MyBookLive?!

No, Windows will not combine 2 MBL’s as 1 entity. They are two seperate network devices which need 2 unique network names.
Have you given each MBL a unique network name by logging into the MBL dashboard and clicking on settings/system and changing the device name on at least one of your MBL’s? If you have 2 devices on your network named MyBookLive I could see you running into issues like this.