Separate other router via VLAN

Yes, the interface should be eth1.30 as it is connected to the CPU handling the lan ports.
A few more things.
You can change the dns under wan6 to some IPv6 ones. Otherwise you have defined them in wan interface already and they are not needed again.

Instead you can use 2606:4700:4700::1111,2606:4700:4700::1001

Remove the isolated_4, it doesn't exist.