Sacha wrote in :

Only a guess but I suspect you've potted them on too swiftly and their
still quite young roots are drowning! Even if you're letting them
drain between watering, they're still hanging about in very wet compost
and too much of it. As the weather is getting colder, the compost
isn't drying out quickly, either.

Thanks, Sacha. If you are right about this, can I save them from dying? Is
there an easy remedy, such as preventing further watering for a while? I
could move them indoors for a few weeks to allow the compost to dry out.

TIA

AL