Grouping instruments

I’m learning to make flexible arrangements. They have other groups then normal: group 1 (Part 1) is flute/oboe, Bb Clarinet, Bb Trumpet; group 2 (Part 2) is Bb Clarinet (2nd), Bb Trumpet (2) Eb Alto Sax; group 3 (Part 3) is Bb Clarinet (3), Bb Tenor Sax, Eb Alto Sax (2) etc etc.
I can’t setup the score like the sample (a Hal Leonard score), I don’t know what I’, doing wrong.

You can’t yet add protruding brackets to the left of the staff for groups, at least not natively.

If you’re referring to shared instruments, you add an instrument to a player by typing Shift-I in setup mode (with that player selected).