You can create a separate part by... 1) Opening the Parts window... 2) Click the new part button on the bottom right part of the parts window... 3) Add the instruments you want in the new part... 4) Edit that new part and only print that one instead of the individual parts when printing or creating PDFs.
You can go into Engraving Rules > Instruments to tweak how the instrument names are displayed, if you don't like the default.
If you're wanting to actually combine all of the parts so that they'll appear on a single staff, you can experiment with the ";Reduce"; plugin, which has several options that will allow you to reduce those three staves to one. The Concert Band Combo has all three of those sounds you're using, so you might want to try reducing them to a Concert Band Combo staff, then just put them on the proper spaces with the proper noteheads.
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