In this case, I'm afraid to say that you might not be able to revive it. The orange "moon cactus" is grafted to the green stem. The orange piece cannot live on its own, as it cannot produce chlorophyll. It appears that the green base of your plant has died or dried out. It certainly looks that way. In my experience, the top bit, the orange part will live for a little while, but will go south soon. They are not meant to live forever, they can't really in their configuration, but generally it is the top grafted part that usually dies first.

To maintain the health of the rest of the plants, I'm sure the other forum members will suggest to repot them individually in well draining media in pots with drainage holes.

Grafted moon cactuses are generally easy to come by, so maybe you want to try another go of it? Good luck!

Can't see the 4th plant, but other 2 would be better planted separately. Haworthia will grow well in partial shade, cacti in full sun.

Ninkasi already explained about the grafted one, the top will probably not live for much longer. You could just leave it sitting on top of the mix after cutting of the rotted/dry/dead rootstock, but don't be surprised if & when it goes.

And yes to well draining mix, and containers with drainage holes. The glass bowl without drainage is not suitable for growing succulents.

There is a very similar current thread, check it out for more info & tips-click here-

Thank you all for the advice. I don't know a lot about plants but really want to have some in my home. Live and learn I suppose!

I will be pulling the cacti out of the bowl and putting them in terracotta pots with drainage.

Can you post a photo of the fourth plant? Just curious to see what it is...

Thanks for posting the additional photo. You could probably keep the cacti together if you wanted to. The Haworthia should definitely be separate (as Rina stated above).