Mine fuss like crazy when I open their beaks too. Just try to be gentle.
I am dealing with sour crop right now on a 12 day old getting ready to tube the chick in a few minuets to flush the crop. I have some Medistatin coming in two days. Hoping it makes it in time.
I'm new to chickens but I used to breed parrots. To make sure stuff goes into the crop and not the wind pipe point the dropped/syringe to the chicks right. So if it is facing you you'd hold the chick with your left hand and with your right hand point the dropper to your left which is the chicks...