I agree with tc, it's in the Echeveria agavoides ('like an agave'!!!!!). The Mammillaria will be more easily ID'd when it flowers - often that's the only key to which species it is exactly (there are more than 100).

The one prominently shown is a Peperomia, I think. Is it only the one that you're asking about?

The biggest help would be to gradually move it into more light. The stretched parts won't get better, but the new growth will be sturdier and more compact. After a while you can cut off the leggy part and re-root the top. Getting some perlite or pumice and mixing it with the C&S soil will improve drainage. Rocks at the bottom don't do much.

Hi Gina, no apologies needed:-) people her will chime in on the IDs, it's not a pain at all, and the list is a little less active because it's JUNE, yay, we are all out in the dirt:-) if you don't get a response soon, try this: repost your photos with numbers and just a short request for ID's. That makes it easier for folks to answer. usually you'll get several responses, with each person just IDing a couple plants, rather than one person doing it all. The numbers help make it easier for several folks to each focus on what they know best.