This is a little spoiler if you want to continue feel free to do so but if not then stop reading my comment at this point.
It will be the sister to first to know about his brother's kid and about the uke being an Omega. She'll have speculations that the Seme will totally disregard and insisted to his sister that the uke is a beta and that he was bonded with a beta so his pheromones disorder won't be cure cause as we all know beta dont produce pheromones but the sister will investigate even the incident in the hospital. The sister warned her brother that he will eventually regret not letting the uke explained the situation and hear him out clearly. Anyways you will love the Seme's sister and so as his family they will welcome the uke and his child. The Seme will make a contract with the uke in return he will help in participating for making an antidote for his condition. (Cause the obviously the uke doesn't want to get back with him thus he doesn't want to sleep with him and sleeping with him will help the Seme cure his condition.) But don't worry those two will be able to sort things out and be together eventually.
I don't know what his disease is or what problems he has but yah bitch u deserved it