You need a new "brake specialist". The brakes on the F53 chassis are rated for the GVWR, which is the total amount of weight that can be carried on the chassis.
The first thing I would do is take the motorhome to a Ford truck dealer or independent truck shop and have the brake caliper slides lubricated and the system flushed and replaced with new fluid. The longer the brake fluid stays in the system the more water it absorbs. When the water content rises to about 3% the fluid is considered saturated. At that point it will boil at about half the temperature of fresh fluid. A spongy brake pedal is usually due to boiling fluid or air in the line.
The burning smell is usually due to brake pads that don't totally release from the rotor. This is where lubing the caliper slides comes in. They must be free of crud and rust to allow them to move as the brake pads are applied and released. Ford recommends lubing the caliper slides and flushing the brake fluid every 2 to 3 years.
2013 Adventurer 32H