Author Site Blogs into Main Blog

Hi! This is probably a simple question, with a simple answer. My terminology may be off, so please be forewarned! I am looking to take all of my user-created sites (on multi-network) and do the following things with their respective blogs:

1. Sort them, based on category and/or tags.
2. Upload certain categories into one subdirectory's main blog, and upload others into the main-page blog.

I understand that there are many ways of going about doing this, but I am unsure which plugins will allow me to aggregate the main-blog, instead of creating a seperate RSS feed (which, as I understand, requires a reader). I want outside people floating about t3h internets to be able to read it without signing in; my main-page theme (divi Extra) has additional means of sorting these on the front end for a pleasant visual experience.

I feel like trying to autoblog my own multi-network is a bit silly, since Post Indexer just lists them all right there. But maybe this is common practice, and I'm confusing the term "feed" as interchangeable between the continuation of an original blog, and the RSS of that blog. Thank you for your patience!