Take a good hard look at the base sections on both plants. Any clues? The plants are rotting from the base up. What does that tell you? Guess what will happen if you continue to grow plants in high organic, slow draining mixes and in a plastic pots without any drainage holes? I hope you enjoy shopping for and buying plants.
That your plants lived for a few years under your cultural conditions is a miracle. Sheer luck.
You can try re-rooting the tops, after the stems form a callous, but if you don't correct that growing medium, you newly rooted plants will also rot, again.
Plants growing in plastic containers need special mixes that drain quickly ....from out of drainage holes in the bottom of containers. Succulents hate having roots growing in stagnant swamps. Roots respond by rotting and taking the top along with them.
Grow succulents in a quick draining mix, in full sun, in heat, and water infrequently with fertilizers. Make sure the container has holes.
Good luck.
