RSYNC and Python Setup

I have one main server and two others that use rsync to sync to one "main" folder. I need to be able to use rsync without entering the password, using keys. So setup two sets of keys for the main server, one on each server... so I don't have to enter a password each time. I know this is an easy task, I just have not been able to complete it correctly. Python... I have python2.7, 3.5 and 3.6 installed on one server. I use a python script that automatically records video streams. However the script is double, triple and sometimes 4x the same recording, this is eating my hard drive. I beleive that python3.5 is not installed correctly, or the three versions are working against one another somehow. I need if possible all three versions of python cleaned and python3.5 installed. Or at a minimum python3.5 installed and working correclty with no cross between 2.7. python3.6 is not required at all...