Update:
The Realband video is misleading at 3:59, where it says just press Generate and Realband will decide based on the selected style, which instruments to use and generate the tracks accordingly blah blah... If you follow that, put in the chords, select a style from Realstyles, and press Generate, nothing happens. If you select the last command "Generate All", then you get the message that it can't regenerate any tracks.
If however, you select the first 8 tracks as BiaB tracks as Rharv mentioned, and then select "Generate All", Realband will generate, starting at track 9 all the tracks it deems necessary according to the style selected, in this case _BBBLUES.

Anyway now I know I can generate tracks individually from track one, or automatically from track 9.

Chris