Take the money order to the police. It will be fake anyway. Don't answer any more e-mail from these people. Now the fake money order has been sent, they will begin to apply pressure to you for the return of their money.
This is how their scam works - they play on honest, good people and convince them (you) that they need their money back, (are starving, have medical expenses, a sick child, a death in the family) whatever they feel will work to make you pay up before the money order is revealed as fake.
Don't open their e-mails as it will play on your mind. Understand that they are master manipulators who will beat you with experience every time. Save yourself the heart-brake and self-doubt.