Bridging WAN with Guest wifi

[gorstj]

I am trying to bridge a WAN port (Eth0) with my 5ghz guest wifi (wl1.1) on an AX86u

The purpose is that I want my 'guest' wifi to pickup an external IP address (I can get issued multiple external IP's) but also enable the router to get it's own external IP address (all via DHCP)

When I do the following:

brctl addbr br10
brctl addif br10 eth0
brctl addif br10 wl1.1

Devices connected to my guest wifi get an external IP address via DHCP and get a direct internet connection - great!
My router can not pickup a DHCP address - therefore there is no access to the internet from devices connected to the Asus wifi

I think I can get Br10 to get an IP address from:

udhcpc -i br10

But doing the same with eth0 doesn't work.

Is there anyway to make eth0 get an IP address when it is part of a bridge? (I suspect this is the issue and not possible?)
Or, is it possible to use the bridge interface (br10) as my WAN connection? (but I think this may require some major hackery!)

Thanks for any thoughts