They are still small I am guessing just aggression. My two reds didnt work together but got a smaller green and they are fine. I heard its best to keep them as only 1 sev to a tank or a group to develop a pecking order.
I got 3 from a lfs. When they first came in they told me I went to check then out and they had aweful ick and the owner advised against getting them so I did so. I went back a week later and the ick was virtually gone the lfs took great care of them and I bought all 3 on the spot cause I was so excited they looked so great lol. I don't really care if they are paired or not. I'm not interested in attempting to breed lol too much work imo. But if they do then oh well. I really want them to just nice and big and fat so I can put them in my 125.
Unfortunately reds are sexually monomorphic, so it's impossible to say for sure. My pair breed lay every so often but eggs don't make the night so who knows if fertility is an issue or not. My female is way more colorful than the expected male.