There seems to be a basic misunderstanding of networking going on here.
First, you can't have multiple interfaces in the same broadcast domain have the same IP. It breaks layers 2 and 3 of networking. That's why the config you posted in the above doesn't work.
Lokytech is half right - vmbr0 has no interface attached to it, and so it will
never be able to pass traffic directly out of the proxmox node it sits on - it will only be able to route traffic internally to another interface. Which is what you're trying to do - but this bring me to the below.
Even if you did have an interface attached to vmbr0, you would still have routing issues. See
this post for an explanation, but essentially you have multiple routes to the same subnet with no weight attached to the routes -- and 3 routes each to 10.0.12.{2,3}. Even if you did have a weight attached, traffic for a subnet can only be sent to one route at a time. Period.
If this is the layer 1 config you
absolutely need to work, you need to change the CIDRs of enp129s0f1 and enp129s0f0 to 10.0.12.x/32, and delete the lines where you add additional routes manually. Your Proxmox node (and VMs) will only be able to communiate with 3 exterior IPs - 10.0.12.{1-3}. This means no access to the rest of your network, no access to the internet, and unless you do some a lot more manual routing and subnetting, VMs in different nodes will not be able to communicate with each other.
If you have a managed switch, or 1 or 2 unmanaged switches, we can make this much easier for you by using trunks, vlans, and vlan interfaces. This is exactly what switches are for.
