First peach trees can be tough to transplant and the later in the spring that you have to do it the bigger the trouble. Are the leaves curling up and dying or are the trees? Were the trees rained on and then the humidity remained high for days on end or did it just keep raining for several days without the trees being able to dry out? First contact the nursery you order them from and report as precisely as you can what is happening, so it is on record. Hopefully, you ordered from one of the many that "guarantee" their stock, if this can't be corrected. They may tell you what they want you to do. First of all remove all the fallen leaves. If the leaves look deformed than then start curling up you may have curly leaf a fungal disease that peaches are real susceptible in many parts of north america. If the leaves seem to be acting as I described, get on line and look at what curly leaf looks like. If it is remove all of the leaves as they become infected and remove them, do not compost, destroy them. As the extension says around here, if the trees put out new leaves by late summer then you might be O.K. In that case remove all the leaves that fall and destroy them. Spray with dormant spray. Next year, spray the tree well just as the fruit buds begin to swell with a copper solution or the sulfur-lime solution used by people unwilling to use the copper. Do the same before it leaves out. Remove any leaves in the spring that look diseased as you see them every year. Do not let those trees bear for at least 3 years and you may have saved them. Peaches have a tap root and the older "bigger" the trees the more difficult to transplant successfully. I agree, they are expensive and if it is the leaves I would try to save them. If the tree itself is bending over, call the nursery and complain now and tell them you expect them to honor their guarantee. You may have to fill out a questionnaire and/or submit pictures of what is happening. I wish you the best, but even with all my years of experience I have not been able to save every peach tree I have tended. I hope yours makes it. If it is curly leaf get those leaves off as fast as they catch it.