A couple ways
i) The way you outlined, FW1->FW2->rest of workflowwith FW3 being created as a detour for FW2. This way seems the most natural to me
ii) Does ISIF 7, 2, and 4 FWS do the same thing? If so, you can just have FW1 -> rest of workflow where FW1 can take any ISIF but starts with ISIF=7 and generate all the other FWs using detours.
At the end of FW1, if ISIF=7 then detour with the same type of FW (FW1) again but ISIF=2.
At the end of FW1, if ISIF=2 and symmetry changed then continue with workflow as normal (goes to rest of workflow)
At the end of FW1, if ISIF=2 and symmetry unchanged then detour with the same FW but with ISIF=4.
At the end of FW1, if ISIF=4 and symmetry unchanged pass final structure else pass initial structure.
But it is not clear to me whether it's worth doing it all in different Fireworks in the first place. I understand that there are likely walltime considerations but it might be worth thinking of running the whole logic of FW1/2/3 within a single Firework and not bothering with detour, etc.
Best,
Anubhav