We'll create fresh WordPress site with MU Post to Multiple Blogs installed. You have 20 minutes to test the plugin after that site we'll be deleted.
Creates a metabox on post edit pages, which allows you to select other blogs to post to within a WordPress multisite.
For performance reasons the number of posts is limited to a user configurable amount, and the blog itself can be made indexable by search engines or not.
This plugin was based on another WP plugin: https://wordpress.org/plugins/wordpress-mu-sitewide-tags/