Sync a data folder among multiple My Cloud NAS

Hi, I have yet to purchase them but I am looking at at least three of the WD 8TB My Cloud EX2.

My goal is to run an RSYNC like app so that any of the media updated at any one location will ultimately populate to all of the locations. It does not have to be real time.

From page 69 of the manual it looks like one WD needs to be set up as a master and the 2nd a client.

For my purposes i’d like to get the folder Syncing to work with:

Dynamic public internet IP from isp - DYNDNS available of course. So for the purpose of mapping i could set up something like:

beachouse.selfip.com\WDMYCLOUD\photo

apartment.selfip.com\WDMYCLOUD\photo

office.selfip(dot)\WDMYCLOUD\photo - link limit

No VPN

How can this be done with this hardware?

Thanks