This is interesting!? Please Respond!

My cousin is having a baby by my brother. They are NOT BLOOD RELATED. However, it's really strange because how will I address their child? They didn't grow up together as cousins so they never considered each other as that...My mom side doesn't disagree with their relationship but my father does(My parents are no longer together)..I can tell that they really love each other but the situation is kind of messed up...THEY ARE BOTH ADULTS...I think in their 20s...What do you all think about the situation and their relationship?...Should she get an abortion? How will she explain the situation to the child?