This is almost an unanswerable question; we agree with you that no trees should have died, no matter whether or not they were mistreated in the planting stage, in 3 or 4 days. Since Mr. Smarty Plants does not make house calls (and probably couldn't solve the problem even if we could see it) we will have to appoint you Detective Plants and give you some questions to answer yourself.
Our first step in an investigation is always to determine if the plant is native to the area where it has been placed. In a state the size of Texas, with so many different soils, that can be very important. According to this USDA Plant Profile Map, Quercus texana (Nuttall oak) is not native to Harris County, but is to next-door San Jacinto County so we don't feel that can be a problem.
The next thing is to find out if the trees are actually dead, using the thumbnail test. With your thumbnail and beginning at the highest branch you can reach, make a very thin scraping of the outer bark. If there is a very thin layer of green beneath that outer bark, that branch, at least, is alive. If there is no such green layer, continue farther down the tree in search of the green. If you can't find any, even down close to the roots, that tree is dead. We still would like to find out how that happened but regardless, dead is dead.
Now, dead or alive, you want to determine what caused its condition that could be avoided in the future or what has caused the alarming symptoms and whether they can be fixed. The next step depends on where you purchased the trees. If they came from a reputable local plant nursery, especially a tree nursery, you need to talk to someone there. The ideal situation would be if someone knowlegeable from that nursery could come to your property to examine the trees, where they are planted, etc. If you purchased it from a large chain store or a home improvement store, you will probably have no luck there.
1. You say you planted the trees immediately after they were delivered. Were they showing any leaf symptoms then? Also, did you notice if the roots seemed to be circling around following the shape of the pot they were in? What we are wondering is if those trees were end-of-season leftovers that had stood, perhaps with little care, in containers on the sales lot. Just because you planted them responsibly does not necessarily mean they were properly cared for nor how long they waited to be put on a delivery truck. In fact, are you sure the two trees you received were the specific ones you chose? Without meaning that anything inappropriate was going on, if you ordered two nuttall oaks without tagging the specific ones you wanted, that might have caused some confusion.
2. We would like to point out that transplant shock is always a possibility, but feel that the trees would have had to be already weakened to show problems so quickly after being planted. Trees can sometimes exhibit symptoms of transplant shock years after the transplant has been made. What do we suggest? Patience; if is still alive it will get its leaves out again in the Spring, they are needed to manufacture food through photosynthesis for the whole tree. Do not fertilize! Native plants ordinarily don't need any fertilizer at all, and certainly don't need it shocking the roots and trying to encourage bloom from a tree still trying to keep its roots alive.
3. On the tree with curling leaves, you should consider the possibility that it was already infested with leaf-curl aphids before it came to you. Read this article on Aphids (the paragraph on Damage) from the UC Integrated Pest Management program.
4. The tree with brown leaves will (if it is alive) probably drop all those leaves at once in the Spring and then put on fresh green leaves. Again, patience is the word.
5. If you get no satisfaction from the establishment from which you purchased those trees, buy no more from them. If you decide you want to plant more, wait until January to buy them, assure yourself that the trees are freshly dug and in good health and that you get the ones you have chosen.