The rootstock is likely hylocereus, some other are used but H. very often. it will likely grow some 'arms', and could get quite large. It may also grow some aerial roots that could be snipped off (at least I do, without any harm to plant).

Degrafted cacti should grow on it's own since it is green; it may have been grafted because it is slow grower? - but I don't know anything about echinopsis if that's what it is.

Not sure if the purplish one is G. p. superbum - the leaves are usually quite large and thinner - but it may be, in just not-so-good condition. My plant has 'flatter' rosette.

What are you repotting them into?

might be graptopetulum Murisaki

Thank you all for the suggestions, I'll look into the names.

GreenLarry and Rina, that's exactly what I thought re the grafted cactus, since it's green (I've had grafted cacti way back then, before I discovered this forum, none survives, now I know why), and I don't mind slow grower.

This is the cut top today, is it dry enough? I'm planning on repotting them all this weekend.

They'll be in potting mix I usually use for my succulents, 1 part organics (bagged mix of rice husk charcoal, compost, etc) and 4-5 parts of volcanic rocks. The rootstock part is actually already potted in this mix (pictured on my original post). The others are still in their original pot and medium (pure rice husk). While the rice husk is really light, but I find it dries quickly only on top part and still quite moist deeper in the pot. I've lost a few succulents in that medium.

chuckerfly

Is the rice husk a medium used by growers where you live? (like peat in Canada and US)?

Rina, yes, that's mostly used by growers here. In my experience, pure rice husk (here we have the "raw" or I think it's parboiled as per net infos) as medium presents similar problem like you have with peat, and it's easier for it to grow mold.

There's also the charcoal version. Personally I choose this over the raw one (easier to water, excellent drainage, lighter, but not as prone to mold), but I have never used it on its own as medium for succulents. Not a lot of nurseries have them all the time, it's a lot more common to find the bagged potting mixes (usually they have the mix with less organics for Adeniums, bonsai, etc. and the heavier mix with more organic ingredients for tropical plants, vegetables, etc.). Even so, it's too heavy for succulents on its own, just like your regular C&S mix you have over there I guess.

The more knowledgeable nursery folks (the ones who don't look at me funny when I ask for more specific name of a plant instead of just "succulents" ;p) suggest using volcanic rocks, it's porous, similar to pumice but black in color and the shape rougher. I mix the rocks with the bagged mix (ratio 4-5 to 1), mainly to provide food for the plants as it contains organic materials including fertilizer, usually manure (I water with ground water/not tap and never fertilize. Should I?).

Updates: I repotted these guys a couple of weeks back and give it more sun gradually.

#1 the frilly Echeveria, whose possible is E. 'Curlylocks' for the loose rosette shape, gets more pink, more upright new growth, and showing old scars

#2 Another Echeveria whose species is still unknown to me gets more pink edges and surprised me with several pups hidden beneath the leaves (it's probably too dark to make out in below pic, but there are pups on the stem, need to find those repot photos)

#3 the Graptopetalum I planted at an angle to make the rosette flatter and more sun in an attempt to make the stem grow upright again, not bent

#4 the Echinopsis (sp.?) I just put on top of the potting mix, the Hylocereus bottom already potted up before.

Everything is looking good, but I think your cactus is a Notocactus, not an Echinopsis. Are the spines flat and relatively harmless?

Notolover, the Echinopsis is suggested ID from earlier. I'm having trouble IDing cacti myself.. as for the spines, yes I guess you could say it's harmless. A bit prickly, but nothing you can't handle barehanded. Off to research Notocactus, thanks.. :)

I'm thinking Notocactus uebelmannianus or crassigibbus. You may find them under Parodia. They look similar, but the crassigibbus has yellow flowers and the other has purple flowers.

noto, probably just a typo, but do you mean Parodia?

Yes--I was at the end of my lunch and I winged it. Thank you--I corrected it to avoid confusion to op.

Well, I hope the cactus will be happy and grow then produce flowers so we can be certain of its identity. Thanks again, Notolover and Rina.