1. Cleistocactus strausii

2. Mammillaria backebergiana

3. An Echeveria that has been beheaded.

Realise you haven’t asked about the compost they’re growing in, but, feel I must mention.......it looks way too peaty for any c/s to thrive in. Needs to be cut with at least 50%sieved perlite and maybe a handful of gritty gravel for good measure and pot stability. They may well rot at the base or root if grown in that for too long as it’s far too water retentive. The glass container is also bad. All pots need drainage holes and glass isn’t recommended as a container for any plant IMHO. Sun can bake the roots, dry the mix, create far too much humidity and cause algae growth on roots etc etc. Sorry.

The last plant, some kind of Echeveria will rot in that glass container w/no holes, THE worst possible environment for a succulent, agreeing w/ Greenclaws above. It needs a small clay pot w/a hole to have a chance.

Also agreeing all your soil needs amendment w/ 50% Perlite or it will never be fast draining enough for these plants.

I'm not the OP but thank you for id'ing these! I've been wanting the first cactus for so long and never could find what it was! Already ordered some seeds.