This is what always happens to my C. Muscosa. I'm not really sure how to get that thing to grow roots and keep them there. Am I watering too much, not enough? Is the soil supposed to retain more water? Less water? I would just take. Those pieces with green at the top and bury them up to the first set of undessicated leaves in a well-draining mix and let it reroot. Just don't let it get soggy. I like to use a spray bottle to root succulents.

Yellowing of leaves is usually caused by overwatering - plant being in water retaining soil. White particles are most likely perlite; is it is same material as blue particles - I believe it is perlite discolored by excess amount of fertilizer. Pick white & blue particle, feel them, even try to squish to see if they fall apart the same way - you can tell then if it is same material. Perlite is good, there should be much more of it, but excess fertilizer is not beneficial. I would get all of the soil off the roots, try to shake it off, help yourself with a chopstick or bamboo skewer to pick it/loosen up from the roots. If some still remains & you can't get it off, swish roots gently in a bowl of tepid water & hopefully it will soften up. Let is dry off on some newspaper or paper towel, check the roots. If any are dry or damaged or mushy/dark looking and slimey, cut them off. If you have to make few cuts, you could dust lightly with some powdered cinnamon (not absolutely necessary, but cinnamon is a natural fungicide); then repot into well draining mix in a container with drainage holes, that is not too large. Make sure you put enough mix into the new pot so your plant doesn't sit too deep in the pot. Leave the pot in little shade for plant to recover and don't water for few days - if you had to wash the roots, there is likely plenty of moisture available. If you had to cut most of the roots (or all), do not water until you see sign of new growth. Should plant be 'wobbly' in the new mix, you could support it with few stones or rocks, or a layer of grit as a topdressing. I would get rid of all old soil, good to put in a compost heap.

Leaves that start yellowing and are soft are most often water logged. The most important would be to give it good drainage - pot with drainage holes and very well draining mix. Mounding up the soil is not problem - it actually helps to direct excess water away, but in water retaining mix it helps just a little. Big pot + water-retaining mix = very big chance of rotting. After these are corrected, the plant will need lots of light.

Your sempervivum looks OK, only a bit lacking in light. They can be grown indoors but they need a lot of sun. Your semp has flowered and you are seeing a normal flower stalk. The main plant will now die, leaving the pups around it to continue the plant. You should cut the pups off and let them root as separate plants and repot one back into the pot, otherwise you are going to be left with a gap in the pot and the pups hanging outside. The other one is an echevaria and also showing a litlle lack of light. You can cut the top off it, let it heal for a week and reroot it before planting it back into the pot. Otherwise it will have a long stalk with leaves at the top from now on. Give them as much sun as you can from now on.