[Richard and Rhonda]

Extremely dangerous. Please fix before driving. Check all the things that others have said. Please don't get under the coach without some support such as jack stands or wooden cribbing.

You don't have to drive it to diagnose the problems. One person pressing the pedal and one observing the brake can actuation will tell you a lot. Make sure you look at front and back since there are separate. Also read up on air brake systems, it sounds like your primary circuit is not working, and when the secondary circuit kicks in with pedal acuation, it slams the brakes on. Google Bendix air brakes primer.