Your storage bottles are OK. I would keep them in a cupboard or other location where they're not exposed to direct light.
The solutions will not oxidize. The only reason for filling the bottle for Solution A is so you can measure the amount of
fresh solution that you add during replenishment. If you're not replenishing then it doesn't matter.
The volume of Solution A decreases with use because it's absorbed into the dry emulsion, and carried into Solution B.
You can certainly use it without replenishment until the volume of Solution A falls below the amount required by your tank.
I would suggest getting additional storage bottles and going to a replenishment system when circumstances permit.
Discoloration of Solution A (and sometimes of Solution B) is normal, as mentioned previously, and is of no concern.