You can enter the default values in your Field settings which is useful is you often need to enter the same combination of authors.
This will display the default values in their own "rows".
But it may be counterproductive if there are no commonly used combinations in your case.
You could limit the field to a certain number of values instead of
Unlimited. Then the form element would display the exact number of input fields. This can work if the number of values you need to enter will never exceed some number.
If this is also not acceptable you can use a different widget completely: instead of Autocomplete use
Select list or
Check boxes/radio buttons. You can change that on the
Manage form display page for the content type.
Other than that you can modify the deafault look of your widget through your theme with some custom code.