Can multiple video streams be recorded?

Yes, each source within the same stream will be recorded as an independent file. Each audio stream will be recorded in its own file. Audio and video sources are handled the same way for recording,

You will have to download each recording file for the stream and do the mixing yourself as appropriate.

There is a possibility for a Chrome device running in the cloud to join as a recorder for the purpose of recording. This video shows you how:

https://youtu.be/01GkV-LpYAo