Uke was human child and meet ml but ml used a fake body. Uke tried to create a bond with black hair seme but failed and trying to prove he did love black seme he hooked up with ml.
That faild and bc of a fight uke almost die and bc ml wanted uke to live reveal who they really where and made a bon an became mates. That cut the ties with black hair seme.
Black hair seme on the meantime is trying to become a god but he can't unless the have there mate aka uke and are trying the ritual again. That is why they need him back at the mansion and they are using his insecurities to lure him.
Meanwhile ml is trying to kill black hair and maybe blond too.
And the last part looks like black hair was a childe that wanted revenge on vampires ended becoming one and tried to create a family for himself but due to society stigma the wife and the baby died and maybe because of that he wants to kill ml