Is the vibration present ONLY upon breaking? If you feel the wheel itself might be involved this may help.
I once had a case of a VW car where we could not balance the front wheels no matter how many times they were meticulously taken off the car and balanced on the machine.
The lightbulb moment came when the tyre dealer changed the center hub on the balance machine for a 4 stud attachment. Balanced wheels 100%
Turned out the center hole in the wheels was off!