Don, the one T'stat controls all of your heating and air conditioning but for the engine dash. I would ask, how many buttons are on the T'stat. If four only, this is no longer available and if it fails you must upgrade the roof air conditioner control boards to work with the newer 5 button T'stat.
To change zones with the four button you have to hold down the top two buttons; watch for the 2 to blink. If the rear furnace does not run; check for power.
Keep trying the front furnace, as you may have air in the lp fuel line. I would recommend you have the furnaces serviced before using them and keep the bugs out of the outside vents.
The cooling unit above the bed is probably the roof rear air conditioner.
The coach house and chassis electrical systems are 12 volt. The 8 D batteries should be installed in parallel for the chassis. The house could be using one for the inverter and one for the house and thus not wire together.
Good luck and keep us posted.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7