Do not keep the brakes on all the way down the hill, because when you REALLY need them they will already be too hot to work. Stay in the same gear as climbing the hill, at least, and if you are unsure, drop a gear. If you are in 2 climbing the hill, don't drop a gear. You need some injector cleaner!
If you know how to adjust the brakes, they already should be adjusted before you get to that hill. If you don't find someone who knows how. On the way down, if the bus starts increase speed quickly, with your foot off the gas pedal, step on the brake briskly and in shorts burst to slow down and once the rpms are low enough to down shift, downshift.
If you are capable of driving the bus at 80mph without over reving the engine, that is what I would do, but I have well over 1,000,000 miles of driving,So don't do that.