Hi, I need to see the SRX interface config and to be complete the chassis config as well.
But in a nutshell this should be a sample of what you need, be carefull not to confuse the RETH interfaces with LAG/LACP Interfaces.
FYI: The LAG interfaces need to stay on the same SRX, you cannot configure a single LAG spanning across two SRX's. If you are only using two interfaces in your reth interface you cannot run a LAG. Then you have a simple interface configured as a access or trunk interface on the EX side mathcing your config on the SRX.
In order for your config to work you would need two interface connected to reth0 on one SRX and another two interfaces connected to reth0 on the second SRX as below. These individual pairs will be connected to your AE interfaces on the EX.
SRX Config:
set interfaces ge-3/0/0 gigether-options redundant-parent reth0
set interfaces ge-3/0/1 gigether-options redundant-parent reth0
set interfaces ge-15/0/0 gigether-options redundant-parent reth0
set interfaces ge-15/0/1 gigether-options redundant-parent reth0
set interfaces reth0 redundant-ether-options redundancy-group 1
set interfaces reth0 redundant-ether-options lacp passive
set interfaces reth0 redundant-ether-options lacp periodic slow
EX Config:
set chassis aggregated-devices ethernet device-count 10
set interfaces ge-0/0/0 ether-options 802.3ad ae1
set interfaces ge-0/0/2 ether-options 802.3ad ae1
set interfaces ge-0/0/1 ether-options 802.3ad ae2
set interfaces ge-0/0/3 ether-options 802.3ad ae2
set interfaces ae1 aggregated-ether-options lacp active
set interfaces ae2 aggregated-ether-options lacp active
set interfaces ae1 aggregate-ether-options lacp periodic slow
set interfaces ae2 aggregate-ether-options lacp periodic slow
Hope this helps.