OK. figured it out.
first pic shows the tails. one on the left is lucy and is 50% bigger. we think she might be luke instead of lucy
second pic lucy (luke) is on the right
third pic is lucy (luke)
and forth pic is chickie.
Chickie is the dominate one but is smaller. way more active than lucy.
I have two RIR chicks about 6 days old. One is almost twice as big as the other. I am wondering if she is a he. I can take pictures of the two to post but what part of the bird should take pictures of?