Ok hear me out.
What if Zianna didn't have an affair but, was raped?
I know you are asking why did she keep the baby?
Because, maybe she didn't want his father to find out about him, and people just said it was an affair because come on Garte is a jerk. And another thing what if she kept the baby because at one point she did love her rapist?
What if it wasn't stranger rape but, familiar rape? Like she and Vylad's father dated in high school? Or he changed into a different person? And perhaps raped His wife's best friend? To get back at her? Zianna could have kept the baby because it was the half brother of her best friend's child?
Ok what I'm saying is, what if Aph's dad raped Zianna getting her pregnant, than when Sylvia found out and got mad at him he  left. That's why Zianna kept the baby because after he left she wanted Vylad to grow up with his sister and his brothers? But, Sylvia and Aphmau left so, they didn't meet till high school. I mean Vylad and Aph's dad have brown hair and Aph and Vylad and very close personality's and that's why he went to Aph's house because he knew she was his sister.
That's my look on things.