Correct. SnapMirror is a Full-Mesh system. Each node must be able to communicate with every other node in the cluster peer.
After you added nodes (and the appropriate intercluster LIFs), you need to use the command:
cluster peer modify -peer-addrs <local_ip1>,<local_ip2>,<local_ip3>,<local_ip4>
If you added nodes to both sides, run the appropriate command on both sides
(you may need a -cluster <clusname> on there too)
Then check it with a "cluster peer ping -originating-node <node-01> -destination-cluster <dest-clus>"
It should be able to ping every node in the cluster at both ends