2 voices in 1 sound file

Hi, I have this command:
dim q as string=""""
s.execute(“say -v Karen “+ q + Textfield1.text + q +”-o /Users/maszlagroland/Desktop/sounds/”+textfield1.text+".aiff")

My problem is that I dont know how to use another Voice Actor and say another string into the SAME sound file, i mentioned above.
I would like to have 1 sound file that i can move to other devices, instead of 60 sound files with different voices.

AFAIK you can’t (https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man1/say.1.html).

Maybe you can merge the files afterwards?
And maybe this will help doing so: http://apple.stackexchange.com/questions/148563/merging-multiple-aiff-files-from-the-command-line

Can I include ffmpeg somehow in my xojo app that i would like to upload to the mac app store?

You could include the Libs. But please check for possible legal issues, before you try so: https://www.ffmpeg.org/legal.html