you hardened them off in mid day sun.. i suspect your sunburned the plants that were grown in a greenhouse.. and perhaps never seeing any direct sun ...

last pic... whats is the grey sheen.. did you spray them.. or did they come with spray on them???

contact the seller.. and tell us what they say ..

ken

The plants were not sprayed, but watered from the top since it was hard to get my large watering can to the pot only. Someone said maybe powdery mildew. The other 3 plants have the white also.

Did you inspect the underside of the leaves with the actual brown spots? The uppersides certainly made me think of rust. I agree that you should contact the nursery, send them pictures, and see what they say.

it sounds like it probably is rust if it wasn't there before, but don't worry too much if it did spread to the other plants - blueberry rust is normally pretty isolated, so it's unlikely to have leapt from one to the other. I'd suggest waiting a week or two to make sure that the other plants (or the first one) don't get any worse, and if they don't, that should be a sign that it's okay to go ahead and transplant the rest.