You won't be able to sex them for some time. By the time they reach maturity, most angels will be about the size of a silver dollar in the body area only. That's just a general rule, some will mature earlier, but the vast majority will follow this. With four fish, you could certainly end up with a sorority, but that's absolutely impossible to predict. The only true way to sex them is once they've decided to spawn. The female's tube is thicker in order to deposit the eggs, and the male's is notably thinner. At the much larger sizes, females will be smaller and more uniform in shape (in properly grown specimens) while the males will usually be larger and some will grow crowns called nucile humps on the head. So you probably have a few months if not more depending on how small and their age right now and how well you maintain them. Before they get to sexual maturity, don't be surprised if one just develops a mean streak. They are cichlids and it's not uncommon to have a tank bully in the mix. There is a forum out there dedicate to Angels specifically and there's a wealth of information there.