Can Proxmox cluster be configured with dedicated nodes at Internet
Yes, that is possible. If you are running latest Proxmox 6.x version, no special setup are required. It's running Corosync 3.x with Kronosnet which are unicast. You might still want to add some VPN for extra security layer between your hosts.
For a previous Proxmox versions multicast was used as a default transport. You have to either manually switch it to unicast where possible or add a Layer 2 VPN with multicast support. See this note on multicast: https://pve.proxmox.com/wiki/Multicast_notes.