This description from Square-Enix Support doesn't indicate whether they approve or dis-approve of one key press going to all clients at the same time by a player. The link simply states how to start and play several characters at the same time.
I've been searching every where for an official answer from Square-Enix on this. I've opened a support ticket to ask them. The reason I've done this is because I've had to reset my password four times now since I started multiboxing the game with many accounts. All of my account passwords are secure so the last two times I've played, I've logged in and played each account separately without sending a key press nor mouse click to all clients at the same time and I didn't receive the password reset email. I believe someone monitors the reports, checks out what's happening and if they see the characters acting at the same time, a password reset is given to all of the accounts. Square-Enix probably wants to keep customers so they don't give out warnings or maybe not just yet as they may not be fully decided on this matter.
Has anyone else multiboxed the release of FFXIV on a regular basis and not received password reset emails? I've been playing FFXIV on separate computers and when one gets a password reset email, all of them get it which leads me to believe that their GM team has done the reset based on what they have observed in game.