The bank 1 sensor 1 (driverside front) and bank 1 sensor 2 (driverside back) should be different from each other. Bank 2 sensor 1 (passenger front) and bank 2 sensor 2 (pass. rear) should also be different from each other. If they are the same your cats are bad.
Both banks sensor #1 can be similar to each other and both banks sensor #2 can be similar to each other.
The front sensors read how rich or lean the engine is running. The back sensors check the catalyst efficiency, by comparing readings with the front sensors. So if the front and backs are the same it means that the cat isn't doing anything.
As far as the coolant thing. Your guess is as good as mine. My coolant was pretty low today (none in the overflow and needed almost a 1/2 gallon in the radiator. I havent seen any leaks. So I'm hoping its not the intake gasket :/
What are the symptoms of that?
My truck doesnt run real rough. It smokes a decent amount of whitish smoke until the engine warms up a bit, but its been cold and wet here, so every car is smoking a lot, and its not thick white, just lots of condensation I think. Theres no coolant in the oil or visa-versa.