Q.Snake plant
I have a snake plant indoors in a dimly lit area; it has been doing fine (about 1. 5 yr old) until now. It has mushy bottoms and they appear rotting and fall over. I water this plant only once month. If I do not water, the soil becomes so dry that some of the stalks fall over too. What am I doing wrong? I do not have a lot of natural light in house so, therefore, I thought this plant would work well. Would appreciate your input.

Check the roots for root rot and repot in new potting soil. This article will help:
https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm