In what order to install water filter cartridges and when to replace.

I have your IS200UC +water filter with the Ultracarb candle in one tank and the CN-B2 flouride/metal reduction candle in the other. I understand that the CN-B2 is not cleanable, but should be replaced every 6 months (which is now). In the flow of water from incoming water to the tap, which filter should be in the first tank?

The B-2 is not cleanable because the shell of the candle is not a filter. The Ultracarb filters from outside/in which means the ceramic membrane acts as the first filter stage and traps the solids.
Eventually, the ceramic memrane (shell) gets dirty and plugged and requires
cleaning http://doultonusa.com/HTML%20pages/cleaning_candle.htm when the flow-rate of water has diminished. Both filters, regardless of cleaning, are recommended to be replaced every 600 gallons (6 months for 4 person house-hold). The B-2 should be implemented into the  first filter housing, followed by the Ultracarb filter in the second housing.