for NAT you can use
auto vmbr192
iface vmbr192 inet static
address 10.1.0.1
netmask 255.255.0.0
bridge-ports none
bridge-stp off
bridge-fd 0
post-up echo 1 > /proc/sys/net/ipv4/ip_forward
post-up iptables -t nat -A POSTROUTING -s...
that same way for any bridge there is a snip from my net work config
vmbr0 is public
vmbr10 is my clusters LAN
i just have all the ports hocked up to the same switch
iface eno1 inet manual
iface eno2 inet manual
auto vmbr0
iface vmbr0 inet static
address 64.XXX.XXX.230...
the ips are only masked for this post
so it could be that publicIP3 is not in the same subnet as publicIP1 and publicIP2
and yes
the first 2 nodes work is just the 3rd on that can join