Simply hitting the "Tab" key will allow you to cycle through your controllable units.
This will work with all characters.
In this situation, when you want one specific unit to move separately than the rest, it's better for you to have only one specific unit selected. It doesn't necessarily need to be one of your own.
If you have all of your units selected, the Tab key will cycle through the different unit types which will allow you to cast whichever unit's unique spells, but movement commands will spread to each of the units currently selected.
If you have a single unit selected (any unit will do - even one that you don't control), the Tab key will cycle through the different unit types that you control, but will select each of your controllable unit-types separately and have the ability to send separate movement commands.
As Brewmaster, activate your ultimate. Likely, at this point all three of your ultimate characters will be directly selected.
Select one of them (Wind for instance), hit Tab and Fire will selected. Tab again to select Earth. Execute a move command to move Earth elsewhere.
Click-Drag to select Wind and Fire, then the Tab key will only toggle those two different units and send the same move/attack commands to those two units only.