Hi Lisa,
What you are trying to do should work. It sounds like the app is not able to access those basemaps for some reason. Could you check the following things for me?
1. All the maps in your basemaps group are public
2) The basemaps group itself is public
3) In the configuration panel you have put the name of the basemaps group in the Alternate Basemap Group parameter
4) You have put the name of the user account that own the basemaps group in the Basemap Group Owner parameter
If you still have issues, let me know and we'll continue troubleshooting.
-Allison