How do I customise the Touch Bar to show the volume up button and the volume down button

Solution 1:

You can touch the volume button and start sliding your finger left or right to adjust the volume up or down.

No need to lift your finger.

The same goes for the brightness as well.

Solution 2:

You can change this via a 3rd party app, or you can set it using System Preferences.

From this question and answer: Have touchbar show vol up, vol down, brightness up, brightness down buttons by default

1. Open the System Preferences app.
2. Select the Keyboard option (third row, sixth item or just search 'keyboard' and it will highlight itself)
3. On the first tab (also called Keyboard), locate the dropdown for "Touch Bar shows" and choose "Expanded Control Strip".

This will give you this layout:

Solution 3:

I suggest you to give Pock a try, you can set up the old volume up & volume down key on your touch bar in pock's preferences. Besides, it's a free app !