I don't know if anyone can tell the difference between an Olive egger and an EE chick, since they are both mutts/crosses. "Just regular" could be a pure breed, or you could have other crosses of two breeds that lay brown. Where did you get your chicks? Or did you hatch them and have multiple breeds that could have crossed? I hatched some olive eggers using a variety of hens, and I quickly lost track of which chick came from which egg after hatch. You can put bands on their legs if keeping track is important.
As far as sexing the chicks, sometimes you can tell be the feather color (depending on the breed), but otherwise, it starts to become clear at 4 - 6 weeks. You want to look at their combs (are they growing fast and turning pink or red = rooster), their legs (cockerels generally have bigger legs), and even their stance can be a clue. Later, you can look for pointy feathers coming in around a cockerels neck, and pointy sickle feathers coming out of the saddle area.
A good sets of photos should show the overall bird, and some close ups of the comb and back area. Good luck figuring it out! With some birds it is tricky. I just pulled a 10 week old pullet out of my bachelor pen because I had made a mistake!
