Newborn chick group with two issues

[chickenprince55]

I have a group of four new chicks, two are three days old and are thriving and already big while the other two came a day later and one chick is much smaller and has 40% less feather cover and the other chick is sitting like a ball away from the group of three chicks in the brooder. She is making a lot of noise and looks like she's shaking and when you try and pick her up she'll get up but then walks very low to the ground with her legs wide however I have also seen her walk normal, please help!

 

[chickenprince55]

. As you can see the one on the far left has significantly less feathers and is much smaller,