Networked websites posts on main site

I had to switch to multisite option since single wp cannot have same slugs.
The way I need it to display >> .com/cat1/events and .com/cat2/events
The way it actually displays >> .com/cat1/events and .com/cat2/events-2

SO I’ve been lurking around multisite and its pretty awesome.
Lets say this is my situation:

“mainsite.com” main
“mainsite.com/site2” subsite
“mainsite.com/site3” subsite.

Main site and all subsites have same plugins and theme design.
Every subsite has own categories and posts under those categories.
So what I was wondering is there a way to DISPLAY posts and/or categories from subsites on the main site.

I already tried several plugins and even the “rss feed” way to do it.