Q.fruit trees
I bought several fruit tree seedlings. I was told to just plant them in miracle-gro potting soil until they were big enough to plant in the ground (or keep in a pot, if I prefer). They are dwarf apple, cherry, plum, peach and pear. Only a few ever even turned green but then they just turned brown and the leaves fell off. I live in Hot Springs, AZ and it has been really hot this summer but I have kept them watered. What can I do to fix this? I bought them online and I can’t buy anywhere in town. How can I save them?

Container plants will need daily water. If temperatures are above 85 degrees, twice daily.
It is likely the seedlings suffered from the heat and sun. If the branches bend they may still be alive but if they snap and break off, this is another indicator that the seedlings likely died.
https://www.gardeningknowhow.com/special/containers/container-plant-watering.htm