- Feed coal to both of them from a central coal double-chest by using hoppers that connect from the bottom of the coal chest to the side of the furnace.
- Feed the materials to cook in each furnace by using a hopper from an input chest to the top of the furnace.
- Drain the cooked output with a hopper from the bottom of the furnace into a cooked products chest.
Then put stacks of coal into the supply chest and whatever you want cooked in the supply chests.
Full auto furnace: The furnaces will keep cooking stack after stack so long as you are close enough to keep the chunk loaded, you don't run out of coal, and you still have something pending to cook in the supply chests.