Depending on where you are some shops will sell orchids potted in a foamy sphagnum moss, styrofoam peanuts, or I've even gotten them potted in compacted potting soil directly in ceramic pots with no drainage. Many people I know think they can't grow orchids because of it. I learned long ago to get them out of the grocery store pots as soon as possible.

Others here can probably advise you better, but something I notice right away is the number of straight rotten roots. I would take a scissor sanitized in alcohol and cut those off. Then repot in some good mix in a pot with drainage and keep them in a humid area, or just put a little humidity dome over the top. A gallon ziploc slipped over the pot can work. Keep them watered and hope for the best. A dusting of cinnamon can work as a weak fungicide.

Thanks for your comment. i’ve been persisting with overnight tea soaks - mainly out of fear of doing anything more radical. the plants seem to be reviving, but there are no signs of new roots.

May i suggest you not use cinnamon on the roots it will dry them out. spray or water the roots with a seaweed/kelp solution until you see root growth its a root stimulant. 1 teas to a gal of water. you can get it on Amazon or at a local nursery. hope it helps.

Still on the tea soaking regime. 3 new roots are forming on one plant. So, do I start cutting off the old blackened roots? They’re still firm so I’m hesitating. How long should the new roots be before I pot up the plant?

Abbykatz, as long as it is a fine dusting I've never had an issue, depending on the humidity in your climate it can work well to kill some of the fungi that can kill the orchid, I've saved three orchids this way. I've also talked to other orchid growers locally who use it as a first pass before using stronger methods. Onc again, though, it all depends on your climate in your growing area. You want it to dry the roots a little in order to kill the fungus. Compounds in the cinnamon help as well, while still preserving the orchid's own defenses.

As for the orchid, I would definitely remove that necrotic tissue. It's rotting and can act as a vector for disease to get into your plant. Remember to sterilize your tools in alcohol. I would still wait a bit for those roots to get to a few inches before I potted it up.