One suggestion is to go to
www.autozone.com and look at their repair guides. I don't know what model year your van is, but rear drum brakes haven't changed a lot over the years. You can find diagrams there to determine if the brake is assembled correctly. Do not make it a millimeter shorter.
It sounds like your drum brakes need service - a good cleaning and new springs perhaps.
I'm guessing the two small boxes in the exhaust system are the catalytic converter and the muffler.
If the exhaust is coming out a small hole, this needs to be repaired. There is risk of exhaust gas entering the passenger compartment.
Take it to a mechanic.