Hi Tim, Firstly if you have other hens keep these isolated for a week or so, maybe more, so that anything they have brought with them will show up and won't be transferred to your others.
If you get them through the ex batt rescue website they are all checked before they are re-homed. Any sick ones are held back and medicated before they are put out to new homes. But if straight from the farmer you'll need to check them over yourself. My first lot up North which I re-homed when I moved down here were from the local farmer and they had mites which I didn't notice - didn't know to look for. So it went right round all the others I had too and I had to treat them all when it had got to a recognisable stage - scaly lumps on legs. Some of them didn't make it. The hens I got down here from Jim at Callander are all healthy, although one was just tiny! She's the one that now flies out into my arms every morning
All your birds will be featherless and will need warm dry bedding and shelter. I keep mine inside for a day or so before letting them into their outside run. Sometimes they are wobbly on their legs so are best inside for a bit. They don't always know how to take water or food from a different container than they are used to so I look for the feistiest one and show her how to peck by putting food and water down and pushing her beak into it. They all follow within minutes once she learns. I feed my ex-batts extra food to start with and I gave them porridge oats with milk and honey as well. Rosemary also suggested special chiacken spices but I couldn't find any.
Hope that helps, sounded a bit rambling when I read it over. Rosemary will keep you right though.
Annie