add additional addresses by adding additional reciparray lines:
$RecipArray[$CurIndex ][] = "".(WA_getSavedFormValue('CheckoutWizard_Basic_Default','First_Name')) ." ".(WA_getSavedFormValue('CheckoutWizard_Basic_Default','Last_Name')) ."|WA|".(WA_getSavedFormValue('CheckoutWizard_Basic_Default','Email_Address')) ."";
$RecipArray[$CurIndex ][] = "samplename@sample.com";
$RecipArray[$CurIndex ][] = "samplename2@sample2.com";