You could use a custom column to store the illustrators and translators -- they are arguably not "authors".
Alternatively, you could manually set the author_sort, it is the automatic derivation of author_sort which doesn't include the parentheses content.
Or use the list_re() function to apply a regex to each element in "authors", specifying & as the list separator.
Personally I favor the custom column.
I would rather separate information that is semantically different.