I think it's not brother complex at all. Dojun is strict with Doyun because, even if he's the only omega, he's still stronger phisically and emotionally than Dojun. To me he looks like someone with low self-steem, who thinks he's too soft for an alpha. He's angry with himself and try to relieve this by being a super controlling brother.
I don’t think he’s like that because he was genuinely worried for his Doyun that time when he saw him on heat with Taehan. I just think he’s really worried because it’s Doyun’s first ever relationship and he already wants to get married!!
Dojun is hurt because of what Dohwa told him when they were children!! I think since then he wishes to be an omega instead of alpha!! Maybe he’ll end up becoming an omega when he continues to sleep with the Doc ╮(￣▽￣)╭
Especially the way they checked Taehan out!!! And I think that’s why Dojun was worried at first when Dohwa came in!! Because the Doc might think Dohwa is more attractive or something...
But why do I have a feeling that Dohwa might be interested in Dojun or maybe he also has that kind of brother complex like Dojun with Doyun ???