From the info provided, it's really not possible to determine exactly what the problem(s) may be and therefore what you need to do to correct them, but here's a few things to consider:

1) Clay soil has an unfortunate reputation. Yes, it is difficult to work with, can be rock hard when it dries out and may provide iffy drainage. But it also tends to be nutrient rich and also binds applied nutrients (fertilizers). Drainage is probably the most important consideration and hopefully the nurserypeople planting the trees accounted for that - a very wide but quite shallow planting hole and with the top of the rootball slightly above the existing soil surface. Any backfill or mulch should have been used to gradually mound up to the top of the rootball.

2) Timing of the planting. Planting trees in the middle of summer when temps are at their highest is just going to be very stressful and bound to create transplant shock. That's likely what the initial wilting reflected.

3) Adequate watering. I've not used the gator bags myself so don't have any firsthand experience on how well they work. But newly planted trees need a LOT of water and good sized trees planted in high heat in the middle of summer need more than you might imagine - at least 5 gallons per inch of trunk diameter per week. And this should be after the initial planting, wherein both the rootball AND the planting hole have been thoroughly soaked. This practice should continue throughout both the first and second growing seasons in the ground.

I suspect the trees are under drought stress......just not getting enough water. The symptoms you describe certainly fit this diagnosis. Either the original rootball has been allowed to dry out or was not properly hydrated before planting or the trees are not getting enough supplemental irrigation this season. Dig down into the rootball and check - the soil should be just moist to the touch and that moist area should extend all the way down to the base of the rootball, a good 12-18". The deeper the soil moisture extends, the more likely and easier the tree roots will follow and a good, deep root system results in greater drought tolerance after establishment. Mulching properly will also help to conserve soil moisture.

4) Finally, when a plant is under stress, you never want to fertilize it. The roots are unable to metabolize it adequately and it just increases the stress. Trees generally require minimal fertilization anyway - only if the soil tests deficient in particular nutrients or if the appearance of the tree itself indicates a specific nutrient lack, i.e. chlorosis. MiracleGro would not be my first choice.....a slow release granular fert applied throughout the dripline would be better but test your soil first before applying any fertilizer. Fertilizing when not needed is often worse than not fertilizing at all.

FWIW, 1.5-2.5 inch caliper trees can hardly be called seedlings :-) Water appropriately for their size and your climate!!

Any mulch at all? Spray round up on grass within 5ft circle (becareful not to get on maple leaves). Wait a week or two for grass to die. Repeat if needed.

Spread 1 inch of compost in that circle followed by 3 inches of aged hardwood mulch (no colored/dye type please).

Water in with a mixture of fish hydrolized fertilizer, humic acid and seaweed liquid every few months in that circle. That will ramp up soil biology activity that will greatly improve the compacted soil. NOT THE SAME as synthetic fertilizer! Organic fertilizer feeds soil microbes including beneficial fungi and bacteria that will multiply and gradually open up compacted soil. If you don't have earthworms, find some to put in the mulch to aerate the soil to improve drainage. I did that and they sure helped a lot. My neighbor 3 houses down the street did not have a single earthworm when I helped planted a couple trees. Huge difference between us.