You can set each of the three output streams to point to different streaming servers for different stations. But the audio carried on the streams will be the same.
If you need three different audio streams going to three different stations then you’ll need three instances of LibreTime (probably each of them running on their own server, VPS, or container). You could schedule each of them to provide different programming, station IDs, or other content at, say, 13:00-13:55, and set up a webstream source for 13:55-14:00 to receive shared content (eg. the news) from a fourth instance of LibreTime. Seems like a good way to set up a network with individual affiliate stations…