If you don't want to us Calibre-epubsplit PI
Use any version of Sigil to adjust files so 'a book' does not share a common section file (use Sigil Split).
Make 5 copies of the original EPUB file (rename each copy to reflect the end results books name)
Use Sigil to delete all but the desired 'book' from each of the saved EPUB copies. Adjust the TOC as needed
BTW use the latest Sigil if you don't have a compelling system reason .
It really has improved since 5.3