I never saw so much of that transparent mucus before!
I believe it could be bacteria or fungus.
Try to gently remove by slow blowing the mucus away with a small powerhead first.
Place the powerhead far from the polyps, so you don't damage them with the water jet.
If the powerhead doesn't work you probably would need to brush it away with a soft tooth brush and take advantage to remove the mucus from the quarantine by syphoning it with a small tube. That way you'll export most of it from the tank. Be careful not to hurt the polyps with the tube, when sucking water/mucus out.
The less you need to brush the polyps, the better chances you'll have ten to come back.
Don't think just because it's a soft tooth brush it wouldn't hurt them.
If the brushing doesn't work easily please stop, because the internal damage will turn things worse. Do not press them too much. It should work within the first attempt.
If you would like to try suck the mucus directly from the polyps you'll need to use an air tube for that and still avoid to touch the polyps to avoid damage on them.
I would do that and do a fast dip in Lugol solution/water or any other iodine or iodide solution.
That would be my first attempt. You can have the solution mixed with tank water or fresh water. Up to 5 drops of Lugol in a small container (8 - 10 oz) with water would do it.
The time for the first dip would be about 30 seconds to a minute max., considering the clean polyps, without any visible mucus on them.
Your polyps are already stressed out!
Good thing you didn't introduce them in the system.
Try to do a water change schedule in the quarantine also.
All this will depend on how much you already did to the polyps to try to fight the mucus.
Wait for more replies too.
Perhaps others could have better ideas?
Grandis.