Hello,
It looks like you imported the demo a few times. It is recommended to run import on a fresh WordPress installation. For this you can use WordPress Database Reset plugin https://wordpress.org/plugins/wordpress-database-reset/ The plugin can be used to remove all the existing content and install a new version from scratch.
So do reset the current content, temporarily disable all 3rd party plugins, and do import then. Or let us know after the reset and we will do the import for you.
Regards