Convict cichlids

So, I adopted 2 convict cichlids. I was hoping they were a mating pair, but one is picking on the other really bad. How can i tell the sex? The one that is picking on the other is very pretty, has some blue in the dorsal fin and has some long things off the back of the dorsal and anal(?) fins. This one is constantly rearranging the sand. The other one I cant tell what the fins look like as they got picked off.


Is there a way to be able to make sure I can get the opposite sex if I were to buy another one? I would like to have a breeding pair.

Females are way bigger than males. Females also have orange on their sides. The one doing the picking sounds like a male.