First off please note that although you plan to use different themes and plugins, your core content is identical, so search engines can and will figure out that all of these sites contain the same content. So if you proceed, just know that you won't be bringing in much if any organic traffic. Perhaps there is a use case for this scenario, but without knowing more, it sounds like playing with fire and likely to get you either blacklisted on Google or else just so far down in search results that you'll have to have some other reliable source of traffic.
The only way to do what you want is to write your own plugin for the main site. Whenever a post is created or updated on the main website, your code will take that same post content and create or update the same post programmatically on each subsite. The fact that your permalink settings on the subsites would differ is what would make the URLs unique, but the slugs will likely be the same across all sites.
You will need to determine all of the subsites before you start publishing, because if you publish a bunch of posts and then want to add a new subsite, you will either have to copy and paste all existing posts onto the new subsite, or update all existing posts on the main site to push content onto the new subsite.