Wait… is her brother in love with her or something 😭

It's not her real brother, the children are his and the mother is a woman who loved him but he didn't loved her back. He was only with her to cope with the rejection from the FL.

Okay phew I didn’t catch that part about him not being related. They even look alike so I was like wtf is thisss

Well they thought that the best way the FL to stay safe is to become his sister in name only.