Its hard to say really, but I wonder if its too hot and dry where you have them. The hazel preferes semi-shade to grow well.
I find new trees are vulnerable for the first couple of years and need lots of watering to keep them ticking over, after that they pretty much take care of themselves.
They would have probably had some slow release fertiliser already in the compost when you bought them, so I would'nt be in to much of a hurry to feed them, at least for a few weeks but keep the watering up, daily if you can and hopefully they will become aclimatised to their new site.
Good Luck. T bird+