Congratulations on growing all of those from seeds! That is great. What is not so great is that they are etiolated - IMO, they all need much more light. Sorry I can't help with names...

1. Looks like Hylocereus seedlings:). Definitely an epiphytic cacti.

2. Acanthocereus tetragonus aka Fairy Castle Cactus:)

3&4. Both look like Cereus peruvianus seedlings.

Have you ever repotted these cactus?

They look like at some point while growing they weren't receiving enough light. That's why they look like that. The seedlings look pretty good, but need to be repotted deeper. Where there's brown at the base, assuming that area is firm, should be under some mix. I can see roots that should be buried.

I would suggest repotting a little deeper and acclimating to more light. Slowlyacclimate of course.

The pots they're in is good, don't go bigger. You can keep potted together the way they are now. Just plant about half and inch to an inch deeper. That should help:).

Thanks for the help, Rina and Kara! I haven't repotted them since they got that big, but I'll do so this week when I repot my other plants. I'll slowly move them outdoors for the last few weeks of summer.

Wow, I might need a bigger home if they survive and grow to their average size.