I was able to determine why I was having trouble with multiple thermostats. In order for the scripts to work properly, it is mandatory to assign a unique label to each of Nest Devices (on the nest device or in the app). I noticed that "name" field in the scripts was blank. I had not populated the label when installing the Nests because the "where" was unique enough for me (Upstairs / Downstairs), but since I added the label, I now see that "name" is populated with the corresponding label and the EG scripts/macros now work properly.
Incidentally, I still have a problem that the ISY for Eventghost plugin causes EG to lock up when I enable on a Windows 7 machine. Enabling the Nest Thermostat plugin does not cause the issue. I have the same results on two separate Windows 7 machines, but no issue on a Windows 8 machine. If anyone has any ideas how to fix this, I'd appreciate it since I'd prefer to use one of the Windows 7 machines to run EG.
Thanks!