Thanks for reply Sanford..I have moved this thread to Products. Expecting a Solution and help on this.
I don't think you should do this in one flow. Make it two.
First flow - a batch campaign - sends the invitation (plus probably change the program status to "Sent Email" or "Invited" if the email is actually delivered)
Second flow - a trigger campaign - listens to the event registration, a form submit I guess, changes the program status to registered and sends the confirmation email.