Maybe I used wrong terminology. Not to make it complicated, I just wanted all robocopy to be started at teh same time from one source to multilple machines. PARALLEL. It saves time.
If done in SERIAL, it takes a long time for the robocopy to finish.
I shall research on FORK, meanwhile, I hope you get my idea, what am trying to do and using "synchronization" might have confused you all. oops.