How are you passing those NICs to the OPNsense VM? Are those virtual NICs or PCIe passthrough?
Permit promiscuous mode for those port groups. Also if you cannot use PCIe passthrough (recommended) you might get better performance doing all the bridging and switching in ESXi. If this is just a test and you intend to deploy on hardware, eventually, go ahead.
Permit promiscuous mode for those port groups.
You cannot do passthrough?
You must enable that feature for individual cards, first. Host > Manage > Hardware ...
You can assign one PCIe device to exactly one VM with passthrough. That's the point. The VM gets full access to the hardware. That's recommended for a firewall, anyway.You can designate a single interface and e.g. use VLANs for other VMs.