If you are Brailling two vocal lines, or the voices change in any way, you need to identify them, as you've done here. I say better air on the side of being perfectly clear with which part is singing what than hoping the reader will understand.
Quick note about the music heading - use the dropped G parentheses instead of the UEB parentheses. (Section 1.3)
Also, you do not need to enclose the text in word-sign indicators when you're treating it as a music heading. If you're putting "a bit quicker" in the music line, you'll need the indicators, but not when it's centered as a heading. Add a period after it, even though none appears in print, if you keep it as a centered heading.
Hope this helps!