What I've done in the past is this:  1.  Create Child SG with one device in it. 2.  Create Parent SG with Child SG in it. 3.  Create view and specify the lun '-lun 0' etc. 4.  Go ahead and add in luns 2, 3. 5.  Create the second Child SG with device that you want fourth.  I'll explain this in a second. 6.  Add the second Child SG to the Parent SG. 7.  Add the devices and specify the LUN ID.  The reason that I only suggest putting only one device in there is due to the fact that if your desired device order doesn't run in sequence with Symmetrix device ids.  Enabling '-consistent_lun' when you create the initiator groups simply ensures that host lun presentation from each of the FA ports is the same for all FA ports in the port group.
As an example, we'd like to build something like the following  Parent SG Child SG1 = Lun 1,2,3 Child SG2 = Lun 4,5,6  I understand on the init group we must enable lun_consistency option. My question is moreso, what are the steps in order to ensure my luns are assigned according to the configuration we design?  I was looking in Procedure Generator and did not find what I was looking for.
How do we ensure LUN consistency when using Parent/Child storage groups?