Old hens and "water bottom"
There are any number of diseases that will result in the your hens displaying the kinds of symptoms that you listed.
Not all soft-shelled eggs are the result of a lack of oyster shell, especially on older hens, laying softshell eggs it is usually the result of a disease or infection in the hens' reproductive tract.
The two hens now belong to you. You and you alone must decide if the few eggs these two hens do lay are worth the potential danger that these birds pose to the rest of your flock.
In-other-words do what ever it is that you think is best and abide by your decision.
You might give them some Corid in their water for 5 days in case changing soil has exposed them to a new strain of coccidia they are not resistant to yet. Then I would put them on some probiotics (if their food has none) and vitamin supplement for a few days, and then twice a week. Look for lice and mites on their skin, and I would also worm them with Valbazen 1/2 ml orally, and repeat that in 10 days. Feed them a good balanced layer feed. All of that may build up their immunity, and you can watch for any disease symptoms.
Thank you for advice! I was actually thinking about how different the soil is between my friend and myself. Although we're only about 6 miles and we live on the same volcano, her soil is very black, fine, rich soil, mine is very sandy pumice dust. Surely our ground organizims vary as well...
Valbazan is a wormer? I will try all three and keep a close eye.
I am the friend. I am going to check my coop tonight when I get home, but my 6 - one year old hens seemed fine this morning, as do the three juvenile ducks. Could it be something from the ducks? They were in with the hens and rooster for about a week before the two old hens were picked up by Jemezhens.