Yes that is what it is. Is that last one how it looks now? if so cut right back on water. It kind of looks like it's just the big one dying. little ones seem fine??

The last photo is the second head on the 2nd plant. It definitely looks bad! I put a dowel into it this evening and it came out dry. I will try watering more sparsely and investigate roughly how much it needs.

Best is to water thoroughly when the plant needs it. How to tell? I'm going to cheat, as usual, and post a summary I made of what Al (tapla) has said about it. Put it into practice for both plants. Soil is another issue; pics of the soil and the whole plants including the pots will help. Here's a post about soils and water retention that will be very useful.

My summary:

The trouble with relying on how the top of the soil feels is that water retentive soils like yours stay wet for so long that the soil in the bottom 1/3 or even 1/2 of the pot is often quite wet when the top few inches seems dry--wet enough to suffocate any roots in the area by keeping them from the air they need to function.

A great way to check soil moisture is to break a 3/8" dowel in half (an unfinished disposable chopstick or even a wooden skewer will work in a pinch), sharpen all four ends with a pencil sharpener, push a piece all the way through the soil to the bottom of the pot, and wait a few seconds before pulling it out. Don't water unless the dowel comes out free of any soil stains and completely dry to the touch; otherwise, keep checking the pot every day or two until the dowel comes out clean and dry.

If this sounds crazy, you should know that the soil still holds a significant amount of moisture inside its particles that's available to roots even when the soil feels dry to the touch. Having done this for two months, and having neglected to water until few days after some pots felt dry a few times with zero negative effects on the plants, I can assure you that it's perfectly safe for scheffleras.

Thank you guys, all great tips. I think an overwatering + poor soil quality + no drainage combination is doing harm. Do you think it best to re-pot it (to switch to a drainable container, change the soil and see the root situation)?

No drainage?? Growing a plant in a container with no drain hole is pretty much a short road to failure and plant death, unless a bog or water plant. If that's the case, I wouldn't hesitate to repot ASAP with a better medium in a properly draining container.

I'm with gardengal. The watering method I explained won't work without drainage, so I'd get the plant into something with a drainage hole ASAP, even if it means keeping it in a sub-par soil.

The best soil would be a 5:1:1 mix (5 parts composted bark fines (between dust and 3/8"), 1 part peat, and 1 part perlite. If you can't find good bark fines, the next best solution is to pick up a bag of fairly chunky cactus mix and use 50% of the mix to 50% perlite (preferably the coarse kind without much dust.

You need to get all the old soil out of the roots if this is going to work. The easiest way usually to start when the soil is fairly dry, shake off whatever your can, and dunk the roots in a pail or other large container of water, swish it around, and use your fingers, a chopstick, or whatever you have on hand to untangle the roots enough that the soil comes out, kneading it a little as needed. Cut any rotten roots back to healthy tissue, do your best to preserve any fine roots, and use a spray bottle to keep them from drying out while you're working. My guess is that you won't find a whole lot of fine roots, in which case most of the soil will fall out on its own.

If you find a bunch of thick woody roots circling the pot that don't have fine roots attached to them you can cut them off with sterilized scissors or shears, but at this point that's less important than getting the plant in a good soil so it can recover.

When you replant, fill the pot about 2/3 full (depending on the size of the root mass), spread the roots out on the mix, then add more mix a bit at a time, using your chopstick or whatever works to fill all voids in the roots with the new mix. I find it helps to whack the side and bottom of the pot every little while to help things settle in place. Stick the roots in a bucket of water or cover them with damp soil if you need to stop the process at any point..

When you're all done water well, making sure to cover the whole surface of the mix. Put the plant somewhere it will get indirect light and don't fertilize until you see new growth, at which point you can move it in front of a window they gets direct sun. The leaves should stop yellowing almost immediately, but it may be a while before you see a lot of improvement because the compromised root system needs to regrow before it can support new vegetation.

Do post pictures of your progress, and don't hesitate to ask for help if you get stuck.

Good luck--I'm looking forward to hearing how it goes and how your little green friend does!