Hi Thornberry, I had a similar experience with my blueberries recently. Not exactly the same problems as yours but I too put them in the soil without amending or acidifying it and applied on it an acidic fertilizer. Surprisingly, all adapted well to this, except one, Misty, which really seemed to be doomed. As a last resort method, I dug holes around the current dripline of this plant and put in sulphur, then spread sulphur around the topsoil and drenched it in water. As the weather has been warming up, I notice new leaves being thrown by this sick plant. In the meantime, I've amended soil around all others with sulphur too and they have nice green leaves. Not as dark green as I've seen in the pictures, but these are in a spot where they get direct sun for 6-7 hours each day, and dappled shade in the afternoon. Net-net: I would not write off your blueberries yet. BTW, I recently visited my trusted nursery and asked the person (whom I consider knowledgeable) the same question: whether it's necessary to plant blueberries in acidic soil in the ground or just apply acidic fertilizer. This person had previously guided me to grow 2 varieties of blueberries in the container and I have had excellent growth for past 5 years or so. He confirmed that, even in the ground, it's not necessary to amend the soil, but it's sufficient to use acidic fertilizer. Just sharing my experience!!

I definitely would not bother potting them up. For fertilizer you can use what you have, as long as it has nitrogen. Other natural fertilizer options include bloodmeal, fish emulsion, manure tea and worm casting tea. When transplanting them out, you'll want to clip off some of the lower leaves and trench them in good soil. Like missingtheobvious said, you'll want to start them in shade and very gradually expose them to direct sunlight. But you'll also want to keep them out of strong wind. Those big leaves are very soft and wind will chew them up, and stems can get crimped at the base seriously compromising the quality of the plant. Below is a link with a diagram on trenching leggy tomato seedlings. Here is a link that might be useful: Trenching Leggy Tomato Seedlings

Yes, the heat can be a concern. They probably wont die unless neglected a long time but heat of 90F will stress them. It can quickly get up to 120 in a greenhouse when it is warm outside. The essentially stop growing much after about 92F (enzymes/proteins) start to degrade. A little heat stress as a hardening process would not be a bad thing (90F for a few hours). Just make sure they have plenty of water, some air movement and the heat doesn't last too long. Warm humid conditions with little air flow could increase disease problems.

They look great. Whatever you are doing, keep doing it. Maybe they are different species? There is at least one other very similar species but it stays a perfect globe--with time obesa gets taller than wide. Can't remember the species name, have seen it at shows.