A Black Sexlink male would have white barring (white lines across his feathers.) He would also have a white or yellow spot on his head when he hatched (this is caused by the same gene that makes the white lines on the feathers as he grows.)
A Black Sexlink female does not have barring, and does not have the spot on her head at hatch. So a person can sort Black Sexlinks by gender just by looking for the spot on the head of the males. That is why they are called "sexlinks," because their is a link between their sex and something else that is easy to see (color/markings in this case.)
Looking at the colors on them, your two chicks are not Black Sexlink males, because they do not have white barring. They could be Black Sexlink females, or they could be males or females of some other kind of chicken.
