Ill take a stab at these to bump the thread.

1 looks like some sort of Cholla to me.

4 reminds me of Euphorbia but I'm not certain about that.

5 I'm pretty sure is some kind of Opuntia

And 6 is definitely Euphorbia lactea variegata which I think goes by the common names of bones and dragon bones

thanks!

1- a monstrous species of Echinopsis (can't recall which)

2- maybe a Cereus species

3- Euphorbia resnifera

4-Euphorbia greenwayi or closely related species

5-another monstrous cactus (Echinopsis?)

6-Euphorbia lactea 'ghost'

I have something that looks exactly like 4, I got it at ikea and it was labelled euphorbia lactea compacta. Take that with a grain of salt as it is ikea, lol.