Mixing public and private IP forwarding

[Patrick M. Hausen]

Configure your OPNsense firewall with one static address from the larger network (/24?) each and the proper default gateway. Forget about the transfer network entirely.

Configure a third address from that /24 with CARP. Configure all remaining addresses as aliases with the same VHID.

Then you can use NAT > Port Forwarding and/or reverse proxies like Caddy or HAproxy to route applications from the external addresses to your servers.