Is it possible to split the video and audio tracks. I want to edit the video track and insert stills and video from a second camera but keep the audio track complete and unchanged
It's much easier to do no splitting at all. Simply drop the stills and second camera video into a track above the main video track. Whatever's higher up in the track stack "hides" what's beneath it. This way since you never edit the main video you never risk changing the audio track.
Yes, simpler just to put stills and video on a higher track.
However if you put video on a higher track you will either have to mute the audio for it, or UNGROUP the audio from that video and then you can delete the audio.