So, depending on the firewall vendor, when the firewalls are configured in active/passive mode, the passive firewall connections are offline until the primary firewall fails. I am thinking That is the reason you don't see ports 5 and 6 coming up.
The other thing you should try is to put all 4 links for both firewalls in the same vlan and test again.
Ok. It looks like neither the ideas I had ended up being the issue.
Before I made the configuration changes on the WAN switch, I turned the secondary firewall back online (I turned it off after troubleshooting it previously). Once back online, all ports were functioning as normal. When I orginally turned it on, I had the ports on the WAN switch shutdown and ran the no shutdown command on both of those ports after the secondary firewall was up and running. Not sure why the secondary port started working and the primary port was off though.
Either way, it works now.
After I had good connectivity, I set all active ports to trunk ports, and applied a native VLAN on ports for their respective ISP traffic. All worked as intended.