Route each LAN port through a separate VPN

I don't have an answer for you, but this thread might help. Configure OpenVPN only on some LAN ports
Note: this thread is a little old, and might not help since vpn-policy-routing is not supported in the latest version.

Sharing the device and type of VPN (OpenVPN, Wireguard?) may be useful for someone to help.

Sharing current config may also be helpful
Please copy the output of the following commands and post it here using the "Preformatted text </> " button:
Remember to redact passwords, MAC addresses and any public IP addresses you may have:

cat /etc/config/network
cat /etc/config/firewall