Hi Mark,
There are a number of ways you can do this - you need to decide on what conditions you want interfaces to fail-over.
In your current setup, you have all interfaces in redundancy group 1. If you add the following lines to your config:
set chassis cluster redundancy-group 1 interface-monitor ge-0/0/4 weight 255
set chassis cluster redundancy-group 1 interface-monitor ge-0/0/5 weight 255
set chassis cluster redundancy-group 1 interface-monitor ge-0/0/6 weight 255
it will mean that when any of the three interfaces go down, all interfaces will fail over to node 1.
You could also configure 3 individual redundancy groups (1,2 & 3) and place one reth in each:
set interfaces reth0 redundant-ether-options redundancy-group 1
set interfaces reth1 redundant-ether-options redundancy-group 2
set interfaces reth2 redundant-ether-options redundancy-group 3
then with interface monitoring configured like:
set chassis cluster redundancy-group 1 interface-monitor ge-0/0/4 weight 255
set chassis cluster redundancy-group 2 interface-monitor ge-0/0/5 weight 255
set chassis cluster redundancy-group 3 interface-monitor ge-0/0/6 weight 255
only the reth that lost an interface would fail over to node 1.
I also like to turn on pre-empt, so that after any failure conditions have been rectified, the whole system goes back to a known topology:
set chassis cluster redundancy-group 1 preempt
set chassis cluster redundancy-group 2 preempt
set chassis cluster redundancy-group 3 preempt
Hope this helps!