How to make a multi-audio video into several video files with one audio track each?
There are several ways to do that. The simplest, but not the best would be to run some sort of remuxing twice, each time taking just a single audio track. But since there is no re-encoding the speed will go down since the computer is forced to read the whole file twice (or more times if you have more audio tracks).

To accomplish the task with a single read using libav (ffmpeg will probably be the same):

avconv -i in.mkv -map 0:0 -map 0:1 -c:a copy -c:v copy out1.mkv -map 0:0 -map 0:2 -c:a copy -c:v copy out2.mkv


It is probably also possible to do that with gstreamer.