Answer:

Note: This feature is only available for EndNote X1 and later.

1. In Windows EndNote, Click on the Edit menu and select Preferences. In Mac OS X EndNote, Click on the EndNote menu and select Preferences.
2. Click on the Display Fields option.
3. If you would like to display all author names under the Author heading in the library reference list, rather than just the first author, select the check box next to Display all authors in the Author field.
4. Click OK.