2019 Honda Odyssey brakes problems

Driving on an expressway, the cars in front of me are slowing down, my car's collision mitigation braking system sends a visual alert with the "brake" signal coming on and I feel the brakes engaging, simultaneously I slam on the brakes, and while there was still distance between the car in front of mine and mine, I am not able to brake. The brakes seem confused, and the impact is so strong that my head almost reaches the steering wheel. The seatbelt is locked in place and leaves me sore.

There is a vibration when brakes are applied on a downhill especially on a 6% grade. Brakes are fine on a straigt non hill and a minor downhill descent.. Vibration seems to occur only when brakes are applied frequently on a steep downhill. Vibration begins with a minor shake than gradually becomes heavy on the shake feeling on the steering wheel and frontal area of van. The front passenger experience the vibration as well. There are 8 passengers on board including our baggage - 4 adults and 3 kids.