Asking for help... Again.

Echeveria Black Prince: Outer leaves are curling up. Is it underwatered or overwatered? Too much or too little sun? Or is it already dying?

Kalanchoe Humilis or "Desert Surprise": Outer leaves are soft, wrinkly, and drooping.

And this echeveria (???) that I beheaded: The stem now has a tiny bud on it but the rosette looks like it's drying out.

And finally, the cactus I was trying to save from the early stages of root rot and cut in half: The cut part seems to have black spots and some of the "tubes" are shrivelled. Is it time to throw this away?