Currently:
Option 1. Add the channels you want to retain relative fader levels of to a DCA. Cons: The individual faders don’t change when you change the DCA master level
Option 2: Create a gang group. Add the channels you want to that and select fader in the options plus anything else you need. Cons: Levels aren’t relative
There is currently no direct replacement for Yamaha’s relative linking functionality as far as I know. A relative option in ganging on suitable options such as fader to allow that would be great though!