Ports and IPSEC passthrough on Orbi?

I believe WiFI calling should work with no port forwarding required, because the connection to AT&T's server should be outgoing, and initiated from your phone.  You would only need to open those ports if your router was blocking the ports on outgoing connections, such as in a corporate environment. Orbi does not block outgoing ports by default.

Also, it is not possible to setup port forwarding for a single port on an incoming connection to go to more than one IP address.  So, doing what you ask is not technically possbile anyway.

If you have tried WiFi calling and it's not working, then you must have some other problem.  For example, if you have Orbi benind another router, that would likely cause trouble.