How do I group Instruments?

sorry, I'm French, and I don't really understand what you want to do. I put a capture of a piece of one of my scores, Is that you want ?

The barline spans for each choir in your score need to be set up using the inspector when you create the score, as previously explained. If you plan to use that particular instrumentation and score layout often, set it up the way you want it, defining any and all special text styles, instrumental choir groupings, barline spanning, staff and system spacing, etc., etc., but without inputting any actual notes or specific text (for text elements, use generic words such as Title, Subtitle, etc.). Then save this blank score to your directory and give it a name such as 'Orchestral Template A' or whatever is appropriate for your needs.*

When you want to create a new work on that template, do not use the 'New Score Wizard' to create a new score; open the template file instead, and edit in the appropriate text for title, subtitle, etc. Then save this modified file under a new name ('Symphony No. 2' or whatever). The template file will stay in your directory unmodified, ready to be used for another piece of the same requirements, and you can then work on the new piece in the usual manner.

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*--Note: If you already have a completed score with all the styles defined as you want them, you can simply save that file under a new name as your template, then delete all the music and replace the text with generic words before resaving it under the template name. That is faster and easier than re-creating the whole template from scratch.