Q.Queen Of The Night “leaves” Turning Brown And Curling – Why?
The plant is potted in a mix of 2/3 cactus soil and 1/3 potting soil in terra cotta pots. I water every other week.

Certified GKH Gardening Expert
I would really like to see the soil, but it looks like overwatering.
It is necessary to check, with plants like this, the moisture content of the soil between watering, AND to allow any extra water out of the container when you do water.
Make sure that the soil dries, very thoroughly, down to 3 inches or so before watering. This will almost never be on a schedule, and will rely heavily on the conditions at the time.
I would make sure that there is no standing water in the bottom of the container at any point. This will cause root suffocation, and rotting.
Here is an article that will help you to care for the plant: