Responses
I dont think doyun likes his older brother if he did like him it isnt romantically because remember what the doctor said that they tried everything so that he will be a normal omega but it didnt work, so the doctor said that I knew it you like that alpha (taehan) that is why he reacts only to taehan, if doyun likes his brother romantically, he would react immediately.
Why do I feel like the doctor is actually an omega or perhaps doyun's brother is also an omega.

soooooo two possiblilities:
1- Doyun likes he's brother ( bc he slept with his alpha who looks exactly like him )
2- ANOTHER SHIP MY HOTHOTHOT DOCTOR AND THE HOTHOT BROTHER TWO ALPHAS AND THAT'S HOT