What soil mix are they planted in? How often do you water?

Agricultural grit and cactus soil pretty much 1:1.

I water when they're dry. About once a week/ two weeks.

Definitely needs more light.

Cracking could be from waterlogging (not very clear pic). Air roots do not mean you have to prune-cut, but you definitely could. Some succulents grow these roots along stems. Often they just dry up, or you could cut them off if you don't like them.

Your plant etiolated a lot, so beheading would be best solution here. But you need to solve the light situation - I remember saying so on your other posts. Otherwise, new plants will grow just the same - etiolated, weak, and color not as good as it should be...Watering should be done when soil deep inside of pot is almost dry (not just top layer). You probably know that :)

Okay will make sure I don't overwater.

Might cut the one that's growing air roots.

Also have removed half of the window cover so they should be getting more light now. This photo was taken on a very grey day!!