I'm no pro on the fridge subject but I would imagine that if the fridge has a level and it reads good you should be ok. As for the house battery it should power all your 12v items,(lights,water pump, furnace blower and such. As for how long that depends on many factors. Battery type and condition and number of batteries being top.
1989 Mallard Sprinter 24' Class C
1974 Shasta XL 2200 TT
2001 Dodge Ram 1500 4X4