What happens when I the technique you described and press 2 (or more) buttons of the same chain? This won't work, right?
I have made some schematics:
Use Reply, then scroll down below the box and use "Attachments and other options" to attach your whatever so we see them. The website image.ibb.co is blocked for many of us.
Do those '4067 breakout boards have bypass caps? If not, you will need to add them.
all the tutorials I have read about the 74HC4067 chips didn't use any capacitors either.
How do I know what value I need and do I really need them?