Probably the easiest way is to use the scheduler to start the main process and the other processes at the same time. If the other processes are logically 'downstream' of the main process then you'll need to add logic so that they can wait until it is time for them to work their queue. (Note that I didn't say sub-process, because a sub-process implies that it is a sub-routine of the main process.)
The only other possibility for having the main process start another process on a different machine is via the command line. But this opens up new complications around resourcing and security, so I'd recommend to keep it simple and use the scheduler and queue logic to orchestrate your solution.