Hi,
I dont think you are understanding RETH interfaces properly, which is why you are struggling with this.
a Reth interface is a redundant ethernet interface. Each SRX will have 1(or more) interfaces attached to a Reth group.
BUT, only one of the SRX's will be active at a time, so only 1 set of interfaces will work at one time.
So SRX A has port ge-0/0/1 in Reth group 1, SRX B will have port ge-0/0/1 in Reth group 1 as well (although the port number will be different in the configuration, physically its the same port on the device).
Traffic can only flow to either the port on SRX A or the port on SRX B, not both.
So, if you would like to create LACP / LG interfaces towards the SRX's, you cannot create 1 group and have all the interfaces in that group, because the inactive SRX will not accept traffic.
Therefore, on the switch you create 2 LACP / LAG groups
group 1 goes to SRX A
group 2 goes to SRX B
I think the problem here is you are using layer 3 port-channels. I cant immediately think of a way to make this work in this manner. What you would need to do is create a VLAN interface on the switch, on both LACP groups put this VLAN on, and on the RETH interface configure this as well