Leave them be. They should have begun to leaf out by now but since they are newbies they may be slow. Mine are just beginning. Don't add potting soil or fertilizer. They are tough plants and will probably be ok.

Ok, I was worried because the ones in the nursery are fully leafed now.

And don't ask that source for advice again. It was just about as wrong as you could get. Leaving it in peace is the best course of (in)action.

If any branches are actually dead that will become evident over time and you can prune them out in due course.

New plants need adequate water since root systems aren't fully established, so periodically stick your finger deep into the soil to see if it needs water.

If the leaves fell off soon after planting in September, it sounds very likely that the shrub did not receive adequate water at planting and immediately after. That could delay establishment and subsequently, delay its spring development.

I agree that patience and adequate watering are all that's needed now,

Haha, yes he wanted me to buy some fertilizer and potting soil. I was weary when he suggested pulling the plant up and putting potting soil but I didn’t wanna be rude so I just kept on nodding as he gave me his advice lol.

I just recently put those rocks. There is a thick layer of mulch underneath. And I installed a drip system for deep watering. I’ll just be patient and wait for them to leaf out.

The barberry can almost certainly stand the reflected heat, but other plants may not be so happy. And Ken, our summer nighttime temperatures are in the 50's so the rocks don't hold heat 'deep into the night'. They barely hold it for half an hour after they are out of the sun. I purposely use rocks for plants that are borderline tender.

Update on the barberrys: they are looking good now, not yet red but probably soon. Thanks for all the advice, folks!