Electron, are you saying that you open the quest giver dialogue, talk to the quest giver with all your characters, get them to the "Accept" window, and then bash the macro?

Or are you saying that you accept on one character then bash the macro to get them all to take part.

The second will always work (ConfirmAcceptQuest). In my experience the first doesn't.

If the first method (all AcceptQuest at the same time) works for you then that's great, but it really didn't work for me, my wife (who also boxes) or apparently for the OP. We'd sometimes end up with two on the quest, sometimes three, and occasionally only one!

I imagine it's down to timing.