cluster srx firewalls interfaces are reth0, reth1, reth2 etc.
the untrust / management interface will be reth0 usually.
& reth1 interface will have the vlans, you should be able to see the isp ip on the reth1 interface logical units
the "show interface terse" on cli will list something like below
ge-0/0/4.557 up up aenet --> ...
I don't have access to a newer SRX, and J-Web has changed substantially in newer versions, but I believe that IP Address configuration is under Interfaces / Ports (eg: completely separated from the chassis cluster configuration).
It may be that your GE interfaces are bound to RETH interfaces and so can't be edited directly, but you can't break a chassis ...