No, as far as I know, AC can't do that directly... The dialogue/speech menu picks the current talking line and write it on the talking character position (or fixed position). But there is not a speech menu item for each talking NPC, everybody is using the same menu textbox.
With custom code It could be done though...
But I think this should be an useful thing... so please... request: more than one speech/subtitle at the same time.
PS. In an adventure I did a long time ago you had to use an object while some characters were having a background conversation... Obviously, you could talk, look at and say whatever you want at the same time... and everyone lines were on top of their character as it should be.
It's possible, but would involve a total re-write of the dialogue system. It's something I've considered before, but it'd be a miracle if nothing broke. I'll at least consider it.
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With custom code It could be done though...
But I think this should be an useful thing... so please... request: more than one speech/subtitle at the same time.
PS. In an adventure I did a long time ago you had to use an object while some characters were having a background conversation... Obviously, you
could talk, look at and say whatever you want at the same time... and everyone lines were on top of their character as it should be.