See "Splitting multiple author names" under Preferences, Tweaks.
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ID: authors_split_regex
By default, calibre splits a string containing multiple author names on ampersands and the words "and" and "with". You can customize the splitting by changing the regular expression below. Strings are split on whatever the specified regular expression matches, in addition to ampersands. Default: r'(?i),?\s+(and|with)\s+'
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