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Yes keep them confined until they know where home is. I also as well as having a hanging feeder put food out in large plant saucers which they eat from until they get the hang of the feeder. My water is just in big dog bowls so that has never been a problem but I have two. Having food and drink in separate areas is good when you put them all in together so everyone has a chance to eat and drink without the oldies keeping the newbies away.

If they are not in with the others yet then they won't be able to watch what they do and get the hang of feeders and ramps and bedtime etc.

When I first had hens they had no idea about perching for ages but since then any newbies we've introduced have immediately jumped on the perch at night, probably because they see the others doing it.

Hmmmm I dunno, because I have a large run where the newbies can run away from the oldies..... in that case probably better then to keep the newbies separate for a few days until they've got the hang of things then put them all in together at night and let them free range together, that way the newbies will have plenty of room to run away . I don't think your old girls had disease I'm sure it's just old age.

My old bat is still going strong at about 5 1/2 years old but she's got a dreadfully rattly chest at times!

A lot of the hen keepers here introduce their newbies at nighttime by putting them on the perch when the others have gone to sleep so might be an idea. I don't have any separate area so mine have had to put up with the pecking and general mayhem.