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This is normally indicative of some type of environmental change, but yellow spots usually mean the plant is being deprived of nutrients. I would first reduce any watering, as over watering is one of the most common causes of leaf yellowing. You should also increase the fertilizer, should the plant be nutrient deficient. In addition, nutrient deficient plants may be a sign that it's in need of repotting. Are there any roots coming from the pot? How is the light where the plant is located? A change in light conditions can also trigger this response. Is it too drafty? You may need to move it. Finally, check the plant for pests. If necessary, you can treat it with neem oil, which should take care of any pest issues and as a bonus, it's also a great fungicide.

Place the moss pole into the pot with the plant. Lightly tie the stems to the pole with string or pantyhose.

The cut will not harm the plant. The fact that there is an infection in the soil will. That is a very large, and now open, vascular cluster. This means that the infection will spread much faster throughout the entire plant. It will be necessary to treat the infection fast in order to save this.

Use dolomitic lime, and wettable sulfur around the area. This will kill off infection, and stabilize the pH. This will offer the plant the best chance of survival.

Just make sure not to water the plant. Unless it is very dry for a long time, you will not need to water this. They are drought tolerant, and will prefer drier soil if you can help it.

From the photo the plant appears to be underwatered, as indicated by the wilting and some dried leaf tips and leaf edges. The yellowing can also be related to the water deficit, and possible nutrient deficiency.

A soil moisture meter can help with taking the guess work out of when to water and how much.

You may be under-watering in order to avoid water spilling out of what appears to be a small tight fitting saucer under the hanging plant.

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm

https://www.domyown.com/luster-leaf-rapitest-mini-moisture-tester-1810-p-7732.html

https://www.domyown.com/dr-earth-organic-all-purpose-fertilizer-p-9485.html

Your photo did not come through, unfortunately, so I cannot see the damage to assess it. I can take a guess at what is causing the issue, though.

Likely, the container is not large enough to support both plants' root systems. This will cause the stronger of the two to take over and kill off the weaker plant.

You may need to separate them, or let the weaker plant die off.

This article will help you with their care: https://www.gardeningknowhow.com/houseplants/devils-backbone/devils-backbone-plant.htm

Unfortunately, your photo did not come through. I am unable to see the damage, but I can take a guess at the issue.

Usually, this is going to indicate overwatering, or bacterial infections. Make sure that the soil is well draining, and does not have a chance to stay wet. Ideally, there needs to be a drain pan to remove excess water.

Treat with a fungicide. This will help treat any residual infections.

Here are some articles that will help:

https://www.gardeningknowhow.com/houseplants/pothos/pothos-plant-care.htm

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm