That's Not Good
I send you two pictures of three cacti that I’ve found abandoned last year. In the past month the big one developed some spots (maybe fungi? maybe a virus?), and both of them have also excrescences growing up from their bodies (same fungi or other parasites?).
Can you please give me some suggestions on how to treat them?
Gualtiero, Liverpool (UK)
It looks like your plants need more sunlight and less water. The tall bluer cactus (Pilosocereus) has a bad infection and should be treated with a fungicide (like Neem Oil, a natural treatment that works and is not resorting to chemical warfare) and then kept dry for a month or two. The smaller green cactus (Echinocereus) has aerial roots, which generally occur if kept too moist and humid. I think you should try finding them a sunnier location and perhaps re-potting in a soil mix that has more “chunky grit”, we use pumice and lava to make up the bulk of our soil, but I do not know if you have access in the UK, but perhaps you can get a gravel based soil mix for alpine plants at your local nursery. Stay away from soils heavy in sand as it retains too much water.
Good luck and take care,