The derailleur was torn apart so I ordered new seat stays and have to exchange (one of them).

I'm not sure how to do it, there are some bearings fastened by screws where hex-wrenches seem to fit on both sides but I am a bit afraid to use brute force and possibly break something.

This is what it looks like: https://goo.gl/photos/Cq8kWhYF8ES3ouBEA

Shall I just try to unscrew that pulling the hex wrenches into opposite directions or I need some special tools?