You can do this with a
Playlist Mixer, which is one of the options on offer when you create a new playlist.
Add each of your playlists under the
Track selection criteria and set it to select 1 track from each:
When you select the mixed playlist MusicBee will only show one track from each playlist, but the key point is that
on completion the cycle is repeated.
Which means after it has played one track from each of the original playlists, it will keep populating the
Playing Tracks list with new ones.
I notice that each time I select the mixed playlist it shows a new pair of tracks. It seems that each time you play it, it starts from where it ended the previous time. Not sure if this is intentional or even desired.
Bee excellent to each other...