I don't like the looks of the potting medium. Does it drain rapidly?

Are you drenching the container on watering day or offering little sips? Watering on a calendar schedule is almost always poor advice. Our containerized plants should be watered on an as needed basis, determined by what the potting medium actually feels like.....how much moisture it is holding.

If it is warm enough I would take it outside and give it a little sunshine. It looks like the short one is getting some fungal die back on the main stem; it looks black. Remember Yuccas grow in the desert. If you need to bring it in in the winter that is OK but I would keep it outside as long as it is warm enough.

"Remember Yuccas grow in the desert."

This particular species though is not native to any desert, it grows in seasonally arid regions of southern Mexico, Guatemala, and into Central America.

When you touch the soil, does it feel dry or moist. I agree the soil appears rich and moisture retentive but looks can be deceiving. It's in a terra cotta pot and we have no idea if the pot is big enough based on the picture. Could be too much water or just as easily, too little at this time of the year.

still alive?